Well, for a start 4% free disk space is a woefully small amount - it's no wonder things are not running well. What size HDD do you have? If you've got a couple of Mb spare, I recommend you download and run a program called
TreeSize from
JAM Software - TreeSize Personal which will help you identify which files and folders are hogging the most space on your disk.
Secondly: how much RAM do you have installed? What are your virtual memory (page file) settings?
The mimimum system requirements for CS and CS2 on Windows are 320Mb RAM and 650Mb HDD space, so if you're anywhere below this then Photoshop won't work properly anyway.