Be careful with MailSweeper - my copy doesn't allow rule exceptions to be used in this way (I use the slightly older version 4.2, V4.3 is the current version).
You can set up a rule to allow mails with .DOC or .XLS attachments - but this will deliver the mail if for example it has three attachments, a .XLS a .MOV and a .DAT for example, because Mailsweeper finds the .XLS attachment and matches it to the 'deliver' rule.
What you can do is limit the number of attachments to one and *then* only allow .DOC or .XLS.
Similarly with images - Mailsweeper doesn't distinguish between a .JPG attachment and a JPG embedded within a Word file.
Pete