Scratch, Partition a second disk, what size?

I've got a new pc, lucky me.
1 gb ram, 2 hard drives. My second hard drive is 120gb in capacity, main drive is 80gb.

I'm using XP, with Photoshop CS, my files size i usually work with arange from tiny to on average 20mb, multiple layers(5 to 6, 120 mb). up to 120 mb single layers maybe 2, max.

I know i don't need 120gb of scratch disk, how much do people recommend as i will partition the disk. And i believe i should use the start of the disk.

Any Advice, suggestions, much appreciated?

I don't like to partition anymore.
I never know when I will fill a partition and I will have to spill contents into another partition, which defeats the idea of the partition in the first place.
In my experience, this is ok with Photoshop, as it just uses the empty space.
William
http://www.williamkazak.com