Of the two jumpers shown on page 2-32, one is a "get-me-outta-trouble" safe-mode jumper and the other is for long-term setting of the CPU type. You'll want to leave J10 capped on pins 1 & 2, and cap the pins on JP11. If you had a CPU that's built for a 100MHz base speed, like a Duron or an old Athlon Thunderbird, then you would pull the cap off of JP11.
Since adjusting the CPU's multiplier doesn't seem to be an option, your alternative is to simply boost the CPU FSB Clock in small steps. Your CPU runs at 2000MHz by default, which is a result of its multiplier and CPU FSB Clock being 15 x 133. Increasing the CPU FSB Clock by 1MHz will result in the total MHz going up by 15MHz because of that 15x multiplier. You may not have a lot of headroom to OC the CPU in this way, because what will happen is that your CPU will hit the wall before your PC3500 is anywhere close to its full potential.
Bigger picture: for gaming performance, especially at high resolutions with antialiasing and ansiotropic filtering, it's the video card you want to focus on first. That also frees up your RAM for your CPU to use, instead of the onboard video and the CPU having to share. I hear the Radeon 9100 isn't bad for a budget card in the sub-$80 range, and should take you up a notch from the onboard video on your MSI.
For the meantime, about that video... go into the BIOS to the
Advanced Chipset Configuration and make the AGP Aperture to be 128MB again if it changed, and the Frame Buffer to be 32MB. Those are the only places where I see the ability to affect the onboard video's slice of the RAM.
On the Compaq, good to hear it's got WinXP Pro. You can Defragment it and uninstall all the Compaq software that you don't actually need, and I bet that will perk it up a little. Setting the user interface for maximum performance (no animations and fancy effects) may make it
look a lot faster. For gaming, it really boils down to the video card a lot of the time, although simulation games and RTS games may be another story than first-person-shooter stuff. Bottom line, if you upgrade the video on the Compaq and it's just too underpowered on the CPU, I'd say it's time to build yourself a new system and carry over the video card you bought.
What do I have the Cheetah avatar for, after all?

I used to be faster when I was on cable instead of dial-up, but I do the best I can
