AdAware SE, SpyBot SD & SpywareBlaster will all work with ME and are all free.
I use AVG Free Home Edition and have used Zone Alarm free home edition firewall successfully on ME.
You should also download HijackThis and install it to the Programs folder. Do a scan and save the Log then post the log on a specialised HJT security forum for analysis.
Don't install to a TEMP folder as HJT needs to make backups just in case you delete something important.