Keep in mind that there are some virus and/or trojan programs out there that don't even have to be opened on the PC in order to do their damage. Simply viewing the message in a preview pane is enough to activate them.
Solution: don't use an email program that uses the IE engine to display HTML mail.
Outlook Express and IE are very insecure.. I really hate running ad aware on family members' boxes, since they're always running a load of malware that IE allows to be installed without even notifying the user.
I like IE but I'm forced to use Moz Firebird on Windows boxen.. I just don't want the hassle of malware any more.