you need a receiver that matches the mic. Then it will run to your interface then to your computer.

I figured that much. What I am wondering is if anyone knows of any receivers out there that can tune into frequencies of that range. I find brand names very expensive.

"Tuning" into the carrier frequency does nothing to demodulate the audio signal riding on the carrier....that's why you have a "receiver" designed for that mic/headset system. In order to do what you think you want to do would require an even more costly tunable receiver with demodulation and would cost you way more than the available "brand name" system receiver as explained by Jack.

Strange, I have tuned in different Brand name receivers to tuners quite successfully, ie, shure with Sennheiser or pasgeo, as long as I had the correct frequency in the receiver, the signal came through fine. I was considering something along the lines of the item below, only tune the receiver to the other microphone. Thoughts?
[[url=http://[/URL]="http://cgi.ebay.com…"]EBAY ITEM[/]="http://cgi.ebay.com…"]EBAY ITEM[/]

Thanks for you prompt replies to people, I appreciate it.

Is the "individual who uses a wireld headset mic", giving a presentation to a live audience, and your recording is a secondary process? Or, are they giving this presentation solely for the purpose of your recording?

If it's a live event, talk to the sound tech (well in advance of the event) and see if there is a feed they could provide to capture the audio. He might rather plug in a cable than run the risk of your rig interfering with his wireless signal.

You could also use a Sennheiser wireless lapel mic such as the one you've linked to as a standalone system. They could be wearing their Shure headset for the benefit of the live audience, and at the same time they could wear a lavalier mic so you could be using your self-contained Sennheiser system to record them simultaneously.

[Any of these wireless solutions leeching off the existing system should be done with the consent and cooperation of the person(s) doing the presentation - and thoroughly tested well in advance of the event.]

A) If you're in the US, you shouldn't be using anything in the 700MHz range. (And you certainly don't want to buy anything new or used in those frequencies, regardless of how cheap it is). The FCC has mandated all users stop using wireless mics between 698 - 806 MHz. If you're an Aussie, you'll have to check what frequencies are used in Aus. (I'm taking a guess as Aus, due to the eBay auction location) The point is, wireless frequency allocation is geographically specific.

B) Sennheiser doesn't try to cover a 200 MHz range that you're asking for 700 - 900 MHz. You have to have a transmitter and receiver from the same "Band" which covers approximately 40 MHz each. *you'll notice there is a slight overlap now with Band G with the newly assigned frequencies.

Senn Band A is 516 - 558 MHz
Senn Band G is 566 - 608 MHz * newly assigned to replace Band C in US markets
Senn Band B is 626 - 668 MHz
Senn Band C is 740 - 776 MHz and would not be available in the States, but might still be available worldwide

Shure Frequency Agile (frequency agile = fancy words for tunable) Wireless Microphone systems (Performance Gear, PGX, SLX, UHF-R, ULX) operate on frequency Bands between 470-698, 944-952 MHz

AKG Band 1 650 - 680 MHz
AKG Bands 2 - 4 have been discontinued in the US because the ran from 680 - 789 MHz
AKG Band 7 500 - 530 MHz
AKG Band 8 570 - 600 MHz

AKG and others use a Tone Code Squelch, which should mute any receiver even on the same freq. unless it receives a specific code in the carrier signal from the transmitter. Another case where you could cause severe interference and drop-outs to the other person's system.

C) The Sennheiser system you link to terminates in an odd unbalanced XLR connector - [ Shield to Pin 1 / Tip to Pin 2 only / no connection to Pin 3 ] which will be difficult to connect properly to your laptop even with a series of unreliable adaptors. Those wireless to wireless systems are intended to be used with camcorders and should also include a 1/8" TRS to 1/8" TRS cable (3.5mm) that I don't see pictured in the auction. It's also a very specific cable that connects to the receiver pack with the locking screw and comes out to a 1/8" TRS type headphone plug. Since the camcorder is looking for right/left rather than a balanced mini TRS, this cable is especially wired to "Y" the T (tip) from the receiver pack to both the T (tip) and R (ring) of the camcorder - that sends your mono signal equally to both left/right. The same would be true connected to a laptop's mic input. But again, you need that specific Sennheiser cable to do that. So have the seller clarify if that's what they're calling the "camera adaptor".

D) You could try a portable "scanner". The type that picks up emergency / HAM radio broadcasts. Many of them can sweep through a range of frequencies, or be programmed to a specific channel, but they were designed for radio chatter not fidelity - so I'd be very surprised if that went really well. The Shure transmitter and receiver would be required to have a label showing their freq. or range of freqs.

And again, any of these wireless solutions leeching off the existing system should be done with the consent and cooperation of the person(s) doing the presentation - and thoroughly tested well in advance of the event.