It's not my PC since I play much higher end games just fine.
My PC specs:
Pentium 4 3.0GHz
Ati 9800 PRO Videocard
1 GIG DUAL CHANNEL MEMORY
ASUS P4C800-E Deluxe Motherboard
Soundblaster Audigy 2 Platinum
120GB WD HD 8MB buffer
Just the act 2 lava area seems a bit sluggish