you don't have to make a new steam account anymore. you can click on "Register a product i already own" and input your ATI key.
HL2/CS:S will appear when they are released
http://www.halflife2.net/forums/showthread.php?t=29636
i upgraded in general. for all games ont he same generation as HL2/Doom3
P4 3.2GHz w/HT
ASUS P4C800-E Deluxe
1GB GeiL PC3200 (512 x 2)
Saphire X800XT-PE
19" Samsung SyncMaster 957DF
120GB Western Digital SATA
Antec TruePower 430WATT
:o