Aside from SpyWare and Virus problems (surfing safely), the most common slow PC complaint is due to the way files are written to the hard disk.  Essentially, files are written wherever the hard disk head can find the nearest open space.  This doesn't mean that that space will be big enough for the file to be written, so what happens is that most files end up scattered across your hard disk.  Loading a single file that is in pieces all over your hard disk takes allot more time than if it were in adjacent spaces on the disk.  In Microsoft Windows XP, you can "defragment" the files on your hard disk using a provided tool.  This will speed up file reading operations and substantially improve your system performance.  Advotech recommends that you defragment your disks weekly.  The following instructions will help you:

To open Disk Defragmenter, click Start, point to All Programs, point to Accessories, point to System Tools, and then click Disk Defragmenter.