Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 3_1_2 like Mac OS X; en-us) AppleWebKit/528.18 (KHTML, like Gecko) Version/4.0 Mobile/7D11 Safari/528.16)
Leopard will work fine, but you'll have to scramble to find all the drivers you will need when Apple does get around to releasing official windows 7 supported drivers it'll be for SL only. So even if you want to stay on 10.5 it may be worth $29 to get the boot camp 3 drivers with SL.
B