MS Word Not Translating Gill Sans to Gill Sans MT and Vice Versa

I have MS Office 2004 for Mac. I don't know where to ask this question but I figure, there are enough intelligent message board addicts here to give it a shot. My problem is summed up in the subject line. When my boss, who uses a PC, sends me a document from Word 2007, she sends it with Gill Sans MT. (No, we cannot change the font family- it's our official typeface.) I get it on my updated Word 2004 for Macintosh in Courier. When I change it to Gill Sans, she gets it in Courier.

Needless to say, with Word's formatting "issues", the font makes a big difference in how the document looks, so this is causing more problems than one might think.

I am not able to find information on which font I need to download so that I can see both Gill Sans and GS MT. Has anyone any idea what might be going wrong? Any advice? Thank you in advance.