The minimum system requirements include a 2.4GHz Pentium 4 or AMD 64 2800+, 512MB of RAM on XP or 768MB on Vista, a GeForce 6600 or Radeon 9800Pro or better, and 8GB of free storage space. In other words, the game is mellow enough that any remotely modern mid-range PC should be fine.
Trine, a puzzle platformer by Finnish developer Frozenbyte, is also steeply discounted on Steam at the moment. The title is $5 (75% off) and has recently been updated with a new level. We'd be remiss not to mention Direct2Drive's spring sale, which has loads of greatly reduced titles.
Grand Theft Auto IV and Supreme Commander Gold are $7.50 each (75% off), Manhunt 2 is $4.95, the Guild Wars Trilogy is $19.95, the Total War Collection is $44.95, and more. Get 'em while they're hot.