Maria, I clean my "temp" files (both Internet and other temp files) once a week. I am using Windows XP Home and here's how I do it:

Click the green "Start" button on the lower left-hand side of the screen (task bar)to access your programs.
Click on "Control Panel" (on left side column with blue background).
Click on "Performance and Maintenance"
Then click "Free up space on your hard disk"
It will take a few minutes for the program to scan your computer. When it is finished a box will appear with all the files you can safely delete. You have the option of un-checking anything you don't want to delete. Once you decide, click on the "delete" or "remove" button (I can't remember exactly what it says). The program will slice and dice again and delete your temp files and also compress your older files to make more room.

When I am finished with that process, I go back to "Performance and Maintenance"
Click on "Rearrange items on your hard disk to make programs run faster"
Then, click "Analyze"
Most of the time, the program will tell you that you don't need to defrag. Do it anyway about once a month. To defrag you just click the "defrag" button and will take awhile (similar to the time it takes to run a virus scan).

Hope this helps and that I haven't confused you too much!