64-bit systems have less need of security software as they are much more secure from serious infections. Rootkits have been virtually eliminated. A reformat in you case was probably unnecessary--either the malware could be cleaned or you mistook a software incompatibility with being an infection--that happens a lot with 64-bit.
See the following thread:http://www.bleepingcomputer.com/forums/t/206774/trojanmalware-infection-vista-64-bit-ie7-moved/
Especially Post #7, which shows shows how to further secure a 64-bit system. Personally, I would stay away from Sypbot's TeaTimer--and actually all of Spybot itself. I would actually only use a 64-bit compatible antivirus (I like Avira's AntiVir, which is free) and MBAM--the rest I'll leave for you to chose. Whatever you decide, just make sure it is 64-bit compatible, which most antivirus software is now.