two 'better than average' free online scanners for malware:

http://housecall.trendmicro.com/

http://www.ewido.net/en/onlinescan/

If you are willing to burn a cd
do a google search for
'Bart's PE download'
or
'Hiren's BootCD 8.6 download'
for a 'bootable' cd that has programs to scan your hard drive without the windows operating system running, which is a better way to detect the worst malware, such as rootkits.