RAID 0 will be faster for loading times. If You are not afraid of loosing anything might as well go for RAID 0. You can create partitions on RAID and You can also create RAID using only part of each disk and use the rest as individual drives or create another RAID( I suppose this could differ on one m/b from other). You might want to look at WD 640 GB drives as they are a bit faster due to higher platter density. And get the one with 32MB cache and 7200rpm. 2 of these
would be a good choice but they are a bit over Your budget. 500Gb will do as well without much difference @ Your budget.