I'm running the pre-release version on my Fujitsu Amilo Pro V3515 laptop. It's got a 1.6 GHz Dual Core pentium chip and 700MB of memory. The S3 graphics card gave it problems when it came to drivers, but I just found a copy of them rather than used the ones windows recommended that didn't work. Otherwise all has been pretty fine with it, except an anti-virus program that wasn't W7 compatible and slowed it down to a crawl. I was running it on 512MB when started and it handled that fine, the upgrade hasn't made a huge difference.
As for XP mode, only program I've found that doesn't work with Win7 so far is Sherston's Tizzy's Toybox, the original version. The SE version is fine. In fact a lot of the old Sherston titles work better now as they don't have that pallette problem that used to leave the graphics messed up if you didn't disable it.