As far as i know, you can not change jumpers of your MB to change the multiplier on p2 Cpu's, since they are mulitplier locked Cpu's. the only way that I know of is to change the front side bus, and most factory made systems (Dell, IBM, etc.) dont have this option. Also it may give you chioces to change the FSB in bios, unless it is a "factory made" computer. You also could try a program called soft FSB which allows you to change the FSB while windows is running on some motherboards, but from my experiece and what I have heared, it doesnt support many P2 boards. Also, if your 350 is running at a 100 mhz bus, or your motherboard supports it, you might want to check out a new cpu, such as a p2-450, Please note though, some p2 boards are "jumperless" for Cpu speed setting to prevent overclockers. If you have an acer motherboard( also used in many IBM Pc's) you may need to download a program from them that will change the bios CPU stepping code if you install a new CPU. This will not allow you to overclock though.
Hope this helps