I suggest anything BUT Outlook/Outlook Express.
Some good alternatives:
Mozilla (with mailnews)
http://www.mozilla.org/
Thunderbird (like Mailnews, only stand-alone)
http://www.mozilla.org/
Pegasus (awesome for when you have tons of email accounts)
http://www.pmail.com/
If you absolutely MUST continue using O/OE, visit the DSLR Security forum at
http://www.dslreports.com/forum/security,1
There, they have an FAQ on email security and privacy:
http://www.dslreports.com/faq/9173 If that doesn't help, make a post on the security forum asking for advice.
A dedicated anti-trojan application is also an option. A/T apps are, as you can guess, MUCH better at picking up and killing evil trojans than any A/V, even Kaspersky. You can learn about some A/Ts at the security forum above.