CS2 vs PSE5

I am an amateur looking for photo editing software for my new computer.

I have a copy of PSE2 that cam with my DRebel and can upgrade to CS2 for $300 until 11/30.

But why should I spend $300 when I can buy PSE5 for $80. I know there are reasons but what are they.

I have been looking for the PSE2 cd for weeks. Had decided I must have thrown it away. My son found it tonight and yes it was in a pile of junk. Sometimes I think I must be getting old.