Hmm. What's your budget? That would be helpful. Cheap can mean different things to different people.
For a room mic you could go with a low cost condenser (quite a few in the low range). Although you can't post currently in the mic forum, you could search and find a lot of useful stuff about these type condensers. One that comes to mind is the Studio Projects B1. I own one and it works well for multiple purposes.
You could also go the dynamic mic route and opt for the
Shure SM58. A decent and standard mic for multiple purposes. I have a couple of these around here and have no trouble finding uses for them.
Then there's Radio Shack.....
As far as getting the mic hooked up to the computer, you'll need some kind of pre-amp or mixer (I say this not knowing what type of sound card/interface you have). A small mixer certainly wouldn't hurt, and that would give you multiple inputs and pre-amps for mics (perhaps). Yamaha makes some nice "budget" mixers. They are the MG line.
I could go on for days here, but I'm not sure of your budget and what you view as decent and cheap. Searching the forums here would be a great start as you'll find a wealth of info on mixers, mics, soundcards, etc. Enough reading to swell your brain maybe....
P.S. The anti-crossposting comment was good advice. When you're posting the same question in multiple forums, it'll be a bitch to keep track of what advice you've been offered and where everything's at - not just for you, but for all of us. Call it fussy if you want.
