The most important thing you can use right now is the "search" function.

Do some homework on this site. If you want the easiest way to waste $1500 bucks then spend it on whatever recommendation you choose that follows this post.
Any recommendation that is given with the parameters you have set forth is absolute BS.
You could also just send me the $1500 and I'll box up some old equipment (ADATs anyone?) with a manual, an SM57, a mixer and a set of headphones. I'll even reply to your questions personally (for awhile)
I've got an old power PC that I'll throw in too.

An iMac might be fine, so might a PC, so might a used G3 or G4. Do some work; read the thread about saving money on audio purchases; browse the DAW forum; etc.....

Well...I will be nice and give you some guidence atleast. You need figure out what kind of system you need, what your wants are. PC tends to be more upkeep and Mac's tend to be a little less up keep but if something goes wrong it is harder to fix (this is all my experience). I personally would go with Mac. I dont think you need to blow your whole bank on a computer. I would go with something that will give you a gig to 1.5 gig of ram. If you are going to be recording your own music and only that then I would go with something a bit cheaper get like a digital audio workstation. You can get a decent one for 500-900 bucks. Then get a couple mics with the remaining money and a cheap audio program. I wouldnt waste all your money on a mac unless you really want to get into audio recording. I hope this helps.