It would appear that you have some form of spambot on your system, especially if you weren't using your email program.
What is your email program ?
What is your firewall ?
A google search for mm5.exe returns many hits, do you happen to be using market maker as that is one of the hits although I can't see why that would be using and email port
http://www.marketmaker.co.uk/aus/index.asp.
First block internet access for mm5.exe with your firewall whilst you investigate/resolve this. XP's firewall can't do this as it doesn't provide outbound protection.
You don't give any details of the trojan detection this helps us to help you.
- What was the virus name, what was the file name, where was it found
example (C:\windows\system32\infected-file-name.xxx)?
If you haven't already got this software (freeware), download, install, update and run it, preferably in safe mode.
1.
Ad-Aware2.
Spybot Search and Destroy3.
Spywareblaster Don't install this until you are clean.
4.
Ewido Security SuiteWhen you are scanning with AdAware or any other security based program it is best to pause the Standard Shield as that program could open a signature file and avast would scan that and may detect a virus signature not a virus and alert. Pausing standard shield avoids possible conflict with the other scanner, avoids duplication of scanning and will speed the original scan up.