You'd of gotten the original Half-Life or Half-Life: Source if you pre-loaded HL2 off of Steam with the silver option. :P
Google is your friend, too.
Bear in mind that this Half-Life story guide is mostly theory and assumptions (not much is know about the story, since you're not told that much in the games), but it is very good and makes sence. Contains some spoilers, though.
http://fragfiles.org/~hlstory//timeline.htm
Enjoy.
- DH