Hmm, I run 7's with my P3-733.
You should be "kicking my behind" with a 933.
Check your CPU heatsink and fan. As the Intel CPU heats up, it can "throttle down" its speed to survive.
If you have AV software running, that will take a huge chunk of CPU cycles. Turn that off, or disable it.
Turn off any power saving settings in your bios if they are enabled. You can power down the monitor, or blank the screen.
Don't power down the CPU, or anything MB related.
Turn off any screensaver in Windows, set it to none.
These are just basic starting points to allow more CPU cycles to be given to S@H. I think it may be heat related.