Steven Hook wrote:

I've got signatures set up on everyone's email in the office, nice
HTML graphicy signatures.
When people using Outlook send to Outlook Express users, all the
images and formatting is lost.
OE recognises it as an HTML email, but looses most of the formatting.

Are you sure it's not being sent as Rich Text?

Additionally, If I forward a message with an attachement from Outlook
to an OE user, the attachment seems lost. It's clear by the message
size that the "data" is still there, but it's not showed as an
attachment. If the message is forwarded as plain text however the
attachment is A-OK.

This is another indication that the message is being sent from Outlook in
Rich Text format because Outlook Express can't handle that format and
ignores any attachment it sees in messages of that format.
--
Brian Tillman [MVP-Outlook]