are you sure your AV/malware/spyware scanners are fully updated? Most new malware will attempt to block all conections to the software vendors update sites upon install (As well as sometimes killing the scanning processes)
When was the last time you did a manual update? and verified it had completed sucessfully? Make sure this is done - then as everyone has said run them in SAFEMODE (normally accessed by pressing F8 during bootup) this should limit what is loaded at startup and should make it easier for the scanners to do their job.
You may also want to give The Cleaner a go (Trojan scanner from MooSoft) as I know Trojans used to be the malware of choice for crackz/warez sites (tho they seemed to have moved onto the more profitable spyware)
But if you are still haivng problems and have done everythin instructed then i STRONGLY recommend backing up your files (lets leave that crack out of the backups tho hrm?) and then formatting the system and reinstalling (am sure you still have that cracked version of XP lying about somewhere )
oh and disable your system restore while doing all this so you dont run into problems later down the road should you get it cleaned up.