Slow and freezing Mac Pro

Hi everyone,
I am using a MacPro running Snow Leopard and keep having increasing problems with a slow operating system and freezing. This initially started when running Photoshop CS1 and Lightroom but now even when both programs are not running.
I reinstalled the operating system, regularly empty the trash and repair system permissions.
Does anybody have an idea where else to intervene as it seriously hampers my workflow now. I am not convinced that it is caused by CS1 being for the PowerPC architecture.
I have a quad core processsor and 4Gb memory.
Cheers,

Chris.

Since you reinstalled the OS and the problem continues, it's my best guess that your hard drive is failing. The fastest test you can try is to use Onyx (free) to check the SMART status. If it says the drive is failing, then a complete failure is imminent. If the drive passes the test, then don't take that as an all-clear. Most SMART reporting tools rely on the drive's own assessment of its health, and the drive manufacturers are highly incentivized to wait until the last minute for a drive to be declared dying. A better tool is Smart Utility. It will do a more thorough analysis of the SMART data and can provide warnings of EARLY failure, meaning you have some time to make plans to replace the drive. The BEST test you can do is with TechTool Pro. It can do a sector scan and check the drive thoroughly block by block.

If that all fails, then you should run the Apple Hardware Test to check for faulty components, or use Rember to do a loop test of your RAM.

Agree with hard drive failure. Boot from your install disc and run repair Disk from there and see what is reported.