I had a whole lot of viruses which brought up a critical system error bubble which takes me to all these sites wanting me to buy softwares etc... I have deleted all the viruses and everything seems to be fine atm except I can't get rid of the bubble and its getting anoying! What can I do?

The type of system it wants me to download is Virusbusters V8.0

Is the bubble advertising a certain brand of antivirus/antispyware? If yes then post it here, this is known malware issue and we might find a removal solution for you.

To add to NK's response.
To make sure everything is running fine run both anti virus and anti spyware apps in normal AND safe modes. (make sure that they are updated first ! ;)) (AVG (http://free.grisoft.com/doc/1) is good and free AV)
(A couple of good removal tools are Spybot (http://www.safer-networking.org/) and Adaware (http://www.lavasoftusa.com/software/adaware/))

ALso an on line virus and spyware scanner is Trend Housecall (http://housecall.trendmicro.com/)

Just a note; actively running two AV's on one machine can cause problems.
So if you are thinking about it make sure your current one is disabled first.
SAme thing applies to online scanners as well.

If this doesn't work can you please let us know more of the symptons and your computers setup.

Critical error are more caused by the damage or complete remove of system files, by viruse or Hard drive Error and sometimes Total machine error. Avg Anti-virus and spyware can remove the viruses but sometimes when a critical error has happened it can occur again if the virus have damaged systems files. In my case it was not viruses but Bad sectors on my computer which would cause a blue screen critical systems error and the way we got rid of it is backup of the drive, When out and brough a new drive and re-installed windows Xp on the new Drive. This idea is only when it gets to be a major problem but if it does re-occur then re-installing windows may be the only way to fix it.

Yes, that would be correct Dchdman,
Daniel, may I ask how many different infections you had and what they were (if you know).

There are some viruses that will delete so many system files, that it isn't worth the time and effort of repairing it (reformat basically... *Dont do it unless you are sure* )

As NK stated, many applications appear to display "Fake Errors" which advise you to download known Rogueware. Rogueware are programs that masquerade as meaningful files, when in reality can be quite malicious.

Virusbusters V8.0 Is rogueware.

Some good websites to help you remove this:
VIRUSBUSTERS.EXE Spyware Remove (http://spywarefiles.prevx.com/RRGDCF28598309/VIRUSBUSTERS.EXE.html)
Yahoo! Answers - Remove critical system error by virusbusters from taskbar? (http://answers.yahoo.com/question/index?qid=20061123103029AALBV16)
Can't Get rid of VirusBusters in Toolbar - Tech Support Guy Forums (http://forums.techguy.org/all-other-software/516125-cant-get-rid-virusbusters-toolbar.html)

Good Luck!