New Harddrive Question

I am looking at getting a 500GB sata drive for christmas. My computer dosnt have sata ports but thats not the problem. My question is that will having a 500GB drive as a boot drive be much worse for a drive of that size than a smaller drive? I plan to partition it but I don't know if that makes a difference. Also whats the common partition size for windows xp pro?

Does windows actually need so much space? I was under the impression that windows xp only actually used about 10 or 15 gbs. I am confused. Also what risk are there in resizing partitions?