Just so we are all on the same page here, I have Mail version 2.1.1 in Tiger.
I created my test .doc file with Word 2004 for Mac. The file consists of text and an inserted picture. OK?
When I attach a .doc to a new message in Mail, the file appears hyperlinked in the composition area. Do you get this too? If I click the hyperlinked file (still composing the email here, don't send yet) it opens as I saved it. I addressed this message to a gmail account and a hotmail account. Send.
I assume you are using gmail in a web browser? I open Safari, sign in to gmail and open the message. I see my file, named as I saved it. My options for the file are to 1)View as HTML or 2)Download. If I click View as HTML, the file spawns a new Safari window and appears as I saved it. Above the displayed file is a link to Download the Original Attachment. Clicking that link gives a little pause, as the file is downloaded. Safari's Downloads window pops up and saves the file to...heaven knows where on my Mac. Luckily I can click on the Spotlight icon there to Show it in Finder. The same thing happens if I go back to the message window and click Download instead.
Once in Finder, I double-click, Word opens, and there is my file as I saved it.
I have Mail checking my hotmail account (thanks httpmail 1.49!). Anyway, Mail displays my new email message, with a hyperlinked file, named as I saved it. Clicking the link opens Word, which opens the attachment as I saved it.
From what you said, this is what you'd expect. Where in that process do you depart from my experience?