they say it can run on rather low-end systems. exactly how well it can run on said systems is the question. kinda makes me glad that i got a P4 2.4Ghz w/ HT, 512MB DDR400 running dual channel (2 x 256), and a GeForce FX 5200 (ya, i know, not the greatest, but get's the job done). also happy about my DVD+/-RW drive just in case it comes on like 6 CD's like UT2k4 did, so then i can try to make it into one DVD. 🙂
Another bit of an update, the high res version of everything shown about HL2 at E3 is at FilePlanet. it's nearly 700MB and contains about a half hour of video.