Photoshop CS3 for Windows painfully slow

Question

I am using Photoshop CS3 on a Windows machine using Vista. It's got a fast dual core processor. Over the last couple months Photoshop has begun operating so slowly that it's practically unusable. I've reset the preferences numerous times. I've upped the RAM in the PC from 2 gigs to 4, and that's offered no relief. I've allocated more RAM to Photoshop. Nothing has helped.
I reached a breaking point today and spent a full day troubleshooting. I've determined that it's a problem with this installation of Photoshop asking for WAY too much scratch disk space. For example, when I open a 2.5meg file on this machine it requires 3.6 gigs of scratch disk space. When I open the exact same file on another machine, it requires only 95 megs of scratch disk space. I have more than four gigs of space available for scratch disk usage on the effected machine, but the fact that it's doing all this reading and writing to a hard drive is killing the performance of the application.
Obviously, there's a problem with this installation of the software. I've tried reinstalling, and that doesn't help.
I called the Adobe tech support line, and they wouldn't touch this questions. They wanted to charge me $39 to even hear what the problem was and then said that they weren't sure they could resolve any issue--especially one like this--after accepting payment. (So, why would I give them a credit card number?) They suggested I post here instead. (Um, great support strategy, huh? I'm a bit frustrated, if you can't tell....)
OK, so off the complaining now. Any ideas for what I can do--short of chucking this PC and buying a new one to reinstall on?

Answer 1

Thanks for the feedback, but none of these things has helped.
I'm working with a recently defragged hard drive with over 35g of free space for scratch disk use. I've done everything in the Knowledge Base post about optimizing CS3, and nothing has worked.
I came across this thread on the same topic from a year and a half ago--and after extensive feedback and testing there was no resolution found to the issue back then:
http://forums.adobe.com/message/1663211#1663211
I'm not holding out much hope here--unless someone from Adobe weighs in since my guess is that this is a software-hardware compatibility related issue. I have a friend who faced this same issue a while ago and ended up solving it by buying a new computer--which took care of the issue.
One more thing I could add that might spark a thought for someone. When I lauch Photoshop, the start up process hangs for about 2 minutes on the step where the application is "Reading preferences." The hard drive grinds away at this point, and I assume it's preparing a huge scratch disk space. It could be that there's a preferenece embedded in the registry which is causing this, but I have no idea how I would go about finding that.
Any other thoughts?