Trojans attached to an e-mail are almost certainly Windows malware, and of no harm to your Mac. (I have yet to hear of Mac malware being distributed that way, though it could happen in the future.)
Of course, you should still delete them, but since spam containing Windows malware is very common these days, it will just come back. Note, though, that you should not allow your anti-virus software to quarantine or delete e-mail messages, as that can cause your mail database to become corrupt. If you are using Apple's Mail, use your AV software to find the file containing the message that has the malware in it, and show it in the Finder. In ClamXav, you control-click the malware in the list and choose Reveal in Finder. The file's name should end in .emlx, and if so, double-click that file to open the message in Mail. (This does not open the attachment!) Then delete or junk the message in Mail.
Good luck!