in all honesty, 7 requires about the same amount of resources as Xp, and less than vista. im running 7 on a e6400(2.6ghz core 2 duo) with 4 gigs of ram, and it runs soo smooth.
windows 7 has a built in virus and spyware remover, called windows security essentials, its caught a ton of shit since ive last installed.
trust me, you wont be disappoint.