Does NIS 2009 Scan prove the system is clean?

If NIS 2009 full scans report nothing other than tracking cookies, does that prove the system is free of viruses, trojans, keystroke loggers -- any type of malware that might have been picked up a month or two ago?

 

I have been running NIS 2009, Linksys router, XP pro SP3 with all updates and IE7.  Upgraded to IE8 last night.  

 

Thanks in advance,

 

Scott