converting .docx files to .doc -- help?

I have a .docx file that I need to change to a .doc file. I'm on Mac OS X 10.5.8, and using MS Word Word:mac v.X

If you don't know how to do this on a Mac (or on my Mac), would someone be willing to take the file via email and convert it for me?

TIA!

ETA: converted by elseperson, fixed now! Thanks all for offers of assistance!