XP Administrator Rights

Much has been asked and written about running Spybot by using the Administrator login (right click, etc.) in Vista. I am using Windows XP and when I run Spybot either in Safe Mode or regularly - it does find malware and trojans - when I ask to delete them - it says I do not have Administrator rights so they are not deleted. Right clicking and asking to run as Administrator does not work as it then asks for a password. There has never been a password associated with this computer - only the regular account and the obligatory "guest" account which is not active. I am now stumped as to how to get rid of the malware and trojans that only Spybot has found - none of the other programs I run find them. Can anyone help ??