Hey everyone I am having this exact same problem. I have clean installs of both the 32 and 64 bit versions of 7 on my home machine, which runs XP really well. My specs are easily better than the minimums (2.2GHz Athlon 64, 2BG RAM, 1GB Video card.
Both installs are virtually unusable because the CPU usage is constantly pegged at 100%. I have installed nothing more than the driver for my graphics card. When there is nothing running, I will open up task manager and it will usually show 50% CPU being used by windows explorer, and 50% by tskmgr.exe. If I open up IE, it will split the three, 33/33/33. Sometimes it fluctuates, but basically all available CPU is always being used up by some combination of the running processes.
I am dumbfounded here. I thought my machine just couldn't hack the 64 bit, but the 32 bit version does the exact same thing. Any help or advice would be highly appreciated.