PC gets bogged down, reboot, bogged down again.

I have a Dell PC s.4 Ghz with 1.0 GB of RAM. In general I have the following applications that run most of the time – Mozilla Firefox, Excel, Auction Sentry (for Ebay), Trend Micro – antivirus, and Adobe Photoshop, and Microsoft Word. The problem I’m having is my performance gets bogged down quickly and then I have to close everything and reboot. The problem is it is extremely inconvenient to just have all these photos I’m working with and then just have to stop everything and start over because the performance is poor. I am open to try whatever may work best. I don’t have any trouble on my Apple Laptops – I have 2 an 867 mhz and a 1.0 GB and both of those machines are faster ALWAYS than my Dell PC at 2.4 GHz. I can do as much work as I like I never have to reboot my Apples.
Any ideas? thanks so much