You can speed up your computer by Overclocking the CPU but its should be done very carefully or you will damage your CPU and the motherboard if you actually want to speed up your computer you can add one more 512 MB RAM if you are using Windows XP it will run more smoothly and if you are using Windows Vista then 1GB RAM is compulsory if your motherboard is using system RAM for display you should buy an Video card and your motherboard even supports the PCI Express card with almost 128MB of memory if you use for gaming or photo editing.
If you can’t afford to buy at present any RAM you can speed up by deleting all the temporary files and even the additional windows temporary files and empty your Recycle bin these may help you in speeding up your computer.