T Mobo I Want To Make My Old Pc Faster By Changing My Processor And Mobo, How Can I Choose One Thats Right For My Pc

I want to make my old pc faster by changing my processor and mobo, How can I choose one thats right for my pc - t mobo

I am currently a reminder Celeron 633, 256, the max. 64MB graphics card. I replaced the power supply of 350 watts or less when the power is no problem. I left the air in my case and have an extra fan for cooling is no problem.
My question is: How do you choose the right processor and motherboard.
I want to go as soon as possible with my old e-machine.
I chose a 80GB HD I need to install the style.
The money is my biggest worry at the moment less is better, but still long for great games with new games. My system is maxed in basically the e-machine, but I think with the right mods, or almost anything is possible. I have plenty of storage space and music and all, but in games like donkey. I need the speed.