I am looking for an antivirus for Windows XP because I am tired of all that s**t that tries to infect my PC. So far I looked into Kaspersky Anti Virus and McAfee VirusScan. Which one is better or should I pick something entirely different?

Avast! AntiVirus and AVG AntiVirus.

Both are free too.

avast is very famous around here... there is a home edition which is free... avg, which not as many use around here also have a free version... like what TwistedMetal have said...
otherwise etrust antivirus provide 1 year free subscription for Windows users... i kindof like etrust too! but not their antispyware...
i use symantec antivirus coporate edition on my system... it is good and i find it a lot better than norton antivirus... which some of my friends are using...
maybe you can buy security suite which have many additional security modules build in such as firewall, antispyware etc... like zonealarm security suite... which comes with a firewall... a antivirus and antispy tool... in additional also IM security and privacy protection...

For commercial AV I wouldn't choose either Kaspersky or McAfee I would instead use eTrust EZ Antivirus, there's a 1 year trial by visiting http://www.my-etrust.com/microsoft/. eTrust EZ Antivirus is the smallest commercial AV scanner I know of, the setup file is only 4.21 MB and when installed it uses consumes about 11 MB.

I would actually choose Avast Antivirus Home Edition or AVG Antivirus Free Edition over many commercial AV scanners that are bloated and install too much. For any OS before Win2k and WinXP I would install AVG, I've seen far too many times with Avast where the resident shield can't be activated in for instance some Win98 systems.

Edit: Fixed typo's.

ezTrust, free for one year.