Well, there are 2 ways you can go with this :"cheap 'n' dirty", or the "right way".
C'n'D: Get yourself a little Audio-Technica boundary mic, model ATR97. This has a 3.5mm "mini-plug" that will work with most minidisc recorders.
$40.00, plus the cost of a Radio Shack 'Y' cord to split out to 2 plugs for the L&R inputs on the recorder. A boundary mic should work very well on the table. It's smaller than a computer mouse (but less likely to crash!) :lol:
"Right" Way: Get an OMNIDIRECTIONAL mic, a decent one, like the ubiquitous E-V 635a (I've seen these on e-Bay for less than $100US). This mic is seen all over TV news shows around the world, as reporters bark into them. Being an 'omni' means that the response is very smooth, with no 'proximity effect' to build up bass when you get closer to it. This is a good thing, because if a musician moves closer to it during a solo, it won't get "muddy" sounding. And, being a real professional piece of gear, it is designed to be tough and reliable. BUT, because of this "pro" status, it is also a "low-impedance, balanced output" device, and as such, will probably not interface directly to your little minidisc recorders' mic inputs. So then we need to get you a....
Mic Preamp (you knew that was coming, didn't you?). Hmmmm... this gets a bit tricky because a lot of the cheaper mic pres on the market are crappy little tube ("valve") circuits designed to be overdriven for "color". I think that maybe M-Audio's "Audio Buddy" ($119.00US) 2-channel mic pre would fit the bill here. It was designed to be used with "pro" mics like the 635a, has "phantom power" available for condensers (the 635a is a dynamic and so doesn't require that), and seems like a good fit for your needs. You can then take the 1/4" output of the preamp and, with the aid of the proper adaper plugs, hook it into the LINE inputs of the recorder.
The advantage of the "RW" is that the mic, being balanced and 'low-Z', will be much less susceptible to noise, hum, and interferences.
So, $50 vs $250 (+/-).your call. Good Luck!

I meant to also say that there are some warnings regarding the recorder. Some minidisc recorders use various forms of "data compression" and this can yield a slightly "grainy" texture to your sound. Others here will be able to detail that aspect, as that is a field I have little knowledge in. I have a Sony from a few years back, and a buddy has one that's newer. Big difference in the sound. Maybe someone can chime in about that.
Also, you want to be sure not to plug an output from a mic preamp into the Mic input of the recorder. "Line level" inputs on the recorder are a must if you use an external pre.

An omni mic will work fine if all you want is a mono result. For stereo, try the Sony ECM MS957. It's a medium-price mid-side electret mic with two width settings and comes with a table-top stand and 1/8 inch plug to go straight into the minidisc recorder. No pre-amp needed.

All minidisc recorders prior to Hi-MD used the ATRAC compression scheme in various versions. Most Hi-MD recorders will record either ATRAC or 16-bit wav uncompressed files. Uncompressed recordings use about 4 times the disc space as ATRAC.

DON'T PUT THE MIC ON THE TABLE.
That's a bad move.
At best the early reflections will sound like you're in the bathroom.
At worst it will create a muddy sound that can not be fixed later.
The mic needs to be closer to the musicians than to any boundry. (wall, floor, ceiling )

You may also want to try something like the Rode NT-4, on a stand in the middle, looking UP, with the capsules point upwards but in a L/R configuration for the room in general.

You may have to move it around a bit (ditto for the players) to find the best spot for the more important instruments, but it's not bad at all - I used it all over Western Ireland back in September on a little tour with some locals there, in Galway, Inis Mor and Ennis.

It runs on a 9V battery, so you can theoretically trick it up with some adapters to go into your MD or other chip-based recorders.

By ALL MEANS, make sure you disable the auto-level function on those things. (Usually hidden many steps down in the menu of most prosumer MD recorders). Auto level is potential trouble for all but the most basic of recordings; it'll make your soft stuff too loud, and your loud stuff to compressed, all the while chomping (and distorting) on peaks. Turn that sucker OFF, if you can, or get a machine that will disable it for you.

Hope you have a grand time yourself!

Thanks to all for good advice here - particularly moonbaby - when you put it as 50 vs 250 bucks, it makes a lot of sense to do things as you say the "right" way

As an alternative to the omni, have you considered using a cardioid in the way that traditional bluegrass players do? I don't know if there is this tradition in Irish music, but there is an old tradition of bluegrass players using a single cardioid mic - often one of those old RCA ribbons - and moving around the stage coming close to the mic during a break and moving away while playing backup. Here they are using the fact that the mic does not have an even response to their advantage. I'm sure it was a technique born of necessity, but I love seeing it performed well and the sound is quite distinctive. Note that I'm not suggesting investing is a ribbon mic (yet), just considering using the technique with a less expensive cardioid. (N.B. - Ribbons are usually figure 8, but the players use only one side, and I've usually seen a cardioid used for the technique today.)

Bob, I've seen that done many times, including the Grand Ol' Opry, and it was a couple of shows on CMT or TNN using a bunch of AT 4050s, 4040s and 4033's that sold me on that line of mics. Five or six acts all worked the mics in the way you describe, and it blew me away at the time.

The sound was natural and a lot more even than I would have ever thought; each soloist simply stepped forward, projected into the mic in the middle, and everyone else simply laid back a bit, both sound wise, and space wise. I started buying AT4000 mics after that, and love 'em to death.

If I'm not mistaken, the "Down from the Mountain" tour was using a bunch of U87's and 67's the same way; everyone working the mics the old fashioned way.

They're a bit too big and bulky to do stealth recording in smaller places like pubs and 'sessions", but when you have the space for 'em, they're worth every penny. Otherwise, you've gotta improvise, which is why I like the NT-4 in a pinch.