I'm putting together my new comp. And maybe because I'm really hungry I just can't decide how big I want to make my System partition... if I just install it in the Disk0 Main space and partition later with Windows Disk Manager is that less good in any way?
Messing with partitions after OS is installed is never a good idea. Given that you havn't installed it as yet, make up your mind now and save a lot of hassles later.
You don't say how big the drive is, assuming it's 320GB or larger around 150GB will give you enough space for the OS, Programs and plentty of room for restore points.
You can store your media, photos and documents on the second partition, so if the need arises to reinstall you won't need to worry about loosing them.
That does not negate the need for backing up any files you don't want to loose onto dvd's that won't be effected by the loss of a failed hard drive.