I have a Schwinn S-30 from the late 90's - the $999 MSRP version, not the $200 Wal-mart version. You should be able to tell just by looking at components. The S-30 had reasonable components, nothing great, but at least Shimano STX RC and some other Shimano parts, Rock Shox Judy XC fork, stuff that a $200 Wal-mart bike wouldn't have.
Take a look at the components on the bike, get some model numbers from them if you can, and post them on here - people should quickly be able to tell you if the bike is crap or not.