If your computer is a pre-built machine, such as a Dell or HP, it will have a model number on the front of it somewhere. You can then look it up on the company website and it will show you what it came with in the store.

My rig is in need of replacement or upgrades, but it's still working for the moment:
AMD Athlon XP 2000+
512mb DDR ram
50GB HD
ATI Radeon 7200 64mb w/tv out
cdrw/dvd rom combo drive
52x cd drive
Sound Blaster Live XGamer 5.1

that's about all I can think of that's interesting...