Open the document in Word 2007, click the Office button,
choose Save As, and set the "Save as type" dropdown in the dialog to "Word 97-2003 document (*.doc)". Click OK. Then send the .doc version.

Actually, you may want to save the file with a .rtf extension, in case you are e-mailing folks who are using programs other than Word. :)

Thanks guys. I actually just opened it from my email at my work computer, copied and pasted it onto a new document and saved it, and then when I attached it to the email it came out as .doc, so problem apparently solved.

Regarding .rtf (rich text format, right?) - is that always the best thing to use, then?

I'm sure others know more details but .rtf is kinda Word-lite. The best to choose depends on what outcome you want. With .rtf, you'll have more of the existing formatting in the converted file.

RTF is probably the most portable format out there -- it's an actual cross-platform standard. You lose a little bit of Word formatting so you shouldn't put in anything particularly stylish if you're doing this, because chances are it will end up looking odd in WordPerfect or whatever.

On the other hand, some places will get an RTF and they'll get all confused and wonder why you didn't attach a DOC like every other sane person. Just be prepared to resend it to someone in as native a format as you can agree on.

DOCX is something Microsoft came up with that, as always, combines something seemingly open (XML and ZIP) in a way that they promise is portable and open, but really isn't, as you're finding.