Can someone help me with clearing it up once and for all? All the anti-virus software I use doesn't work, the spyware programs are only temporary solutions and the other people who use this computer are completely reckless when it comes to surfing and downloading.

Can someone walk me through a complete clean-up? What's the deal with the HijackThis program I've seen mentioned?

Cheers.

Please download HJTsetup.exe from this link http://www.thespykiller.co.uk/files/HJTsetup.exe to your desktop.
Doubleclick on the HJTsetup.exe icon on your desktop.
By default it will install to C:\Program Files\Hijack This.
Continue to click "next" in the setup dialogue boxes until you get to the "Select Addition Tasks" dialogue.
Put a check by "Create a desktop icon" then click "Next" again.
Continue to follow the rest of the prompts from there.
At the final dialogue box click "Finish" and it will launch Hijack This.
Click on the "Do a system scan and save a logfile" button. It will scan and the log should open in notepad.
Click on "Edit > Select All" then click on "Edit > Copy" to copy the entire contents of the log and post it in this thread.

Do not fix anything yet unless you know what you are doing. This is a powerful tool that can crash the computer if used improperly.

Run this free online scan from Panda

When the scan completes, if anything malicious is detected, click the See Report button, then Save Report and save it to the desktop, then copy/paste into the text editor and post it.

Okay, I got HJT but everytime I try to use it (after I click 'Do a system scan and save a logfile') it freezes, then eventually a box will come up telling me the computer will shut down in 60 seconds.

The computer will be on for a few minutes, then automatically reboot. It's annoying.

Could also be the Sasser Worm
You can download the fix here,
Sasser Fix

" Please Post back to let us know if we helped "

To stop the auto shut down do to start> run> type "shutdown -a" without the quotes then press ok. Then run the sasser fix as Bob suggested.