be nicely, you'd better separat your system drive with your data drive. I mean to have a logical C:--for system and D: --for data , and E: for your Cd-Rom.
a good habit to make you system drive clean, and make a lot of space for you windows to cache your start up program. it will make a big difference.
or another way to do is to make your system pagefile bigger. but it is not alway work : double click "system" in your control panel, in "advance" tag, you click a botton for your system virtual memory, then adjust the pagefile to double or three times of your physical memory(upper bound). and restart your computer. to see if it is a little bit better