You don't say how big your hard drive is but if it is getting full it will slow you down. Run CCleaner click here to get rid of all temp files and clean the registry.
Go to Run or Search and type in msconfig, enter and on the Start Up Tab untick all non essential start up items. If you are unsure what is essential then Google it and find out.
If you can afford it add another 1 or 2 Gb of RAM.