Good words, remember though never follow anything like this without a knowlegeable computer person behind you making sure everything goes right... or when it goes wrong can fix it.

Some of the safest ways to speed up your PC (these are partially mentioned in the above guide)

Run a virus checker
Run a spyware checker
Run a software cleanup wizard
Run a defragmentation program

generally if you use good products for each of these there is no risk to your computer.

Sometimes though you just have to upgrade your computer hardware, the easiest thing to do is put more RAM in. Ask your local computer parts retailer and they will be happy to tell you how (or even do it for you as its a quick process)