Hi Cori,
I read your other post and wanted to put my $0.02 in. Background: I'm a new cyclist, and researched ALOT before spending a dime on anything. I thankfully had $500 to work with from a replacement/pitty action over my stolen 1990 era MTB, and really
really looked long and hard into New vs. Used. I ended up getting a new
Lemond for $585 out the door(I did this because I have a 100 mile Century comming up in Spring for a fundraiser). Needless to say, after a few weeks of posting and reading here, along with my girlfriends new interest in riding a cycle with me I've been looking into the USED scene...just as you are doing. Here's my advice, and I hope it helps being a n00b myself:
#1 Be patient, and ride as many used/new bikes as possible to understand what "fits" your body.
#2 LBS...I have a great selection of LBS here, and at first I was really affraid to ask questions, because my knowledge was limited. Now I ask them just about everything about bikes...new ones, frames, USED ones, old school components, etc. I look at the used bikes they have, the components, the prices. It gives me a good idea on what it would take to get a USED bike up to par when I find the right frame. Ask questions to as many staff members at your LBS...your bound to find a bike geek that likes/knows old bikes/commponents and has preferances on them. Knowledge and opinions are priceless when it comes to used/oldschool bikes.
#3 Keep up on the threads here. Read the Vintage section, and look at what people have done with older bikes(some of this amazes me...$45 dollar 10 year old bikes turned into awesome commuting machines for $200 for example). Post questions(as you've done) about specific bikes/frames you come across. Search the net for bikes you find in your price range, and look at the component info.
#4 Dig, search, scavange. Most Police, mass transit, road companies have auctions. For example, I know a guy who got a great used road bike, 10 years old, from the local bus company auction for $10. $150 dollars later, and this bike is as fast as mine!
Also, do the thrift store and yardsale runs. Bikes are like any excercise equipment...people buy them, never use them, let them sit in the garage for years, and sell them cheap. Read the forums, and you'll see people find them all the time. This is my personal hope for a cool bike for my GF and perhaops for me that I can learn some mechanics on at a affordable yet fun price.
Hope this helps...and good luck! Kepp us informed on your search! Many bike folks here are really helpfull...they helped me!
Cheers,
Lufty