You don't really need a high end system to run win 7.Infact if your system can't run windows vista the chances are that win 7 will work fine.
I have three laptops running win 7 RC
1. An old AMD with 512mb ram.
2. A core2duo with 3gb ram.
3. Atom based 1gb netbook.
Performance is better than vista and at par with xp.