How do I partition wd caviar black 640gb before vista 64 install?

I bought 2 wd caviar black 640gb OEM hard disks and I will want to partition them and I've never partitioned before. I will be installing vista 64-bit OEM on one and using the second drive as backup, but not in RAID.

My preference is 2 partitions for each disk, with the primary partition for vista and programs. How large should this be? Should my games be in a third partition or not? The main one will be sims 3.

Since I am partitioning before installing vista, do I need to download the software, as the disk is OEM? Do I just go to the WD website?

Thanks