I've just tried it on my old Dell Inspiron 9200, Pentium M 1.6GHz, 1GB Ram.
Ran much, much better than I expected. As good as, if not better than XP. Of course this is without anything else installed.
Unfortunately I could not get my wireless to connect to my network so I'm back on XP for now. If it wasn't for this I'd be happy to run Win7 on my old lappy!