Can an .xls file contain a virus?

I got an email today from someone I do not know. However, I often get email from people I don't know since I run a couple businesses.

Any email containing an .exe or .pif (or similar) file is discarded without opening.

But this email contains an attached file with an .xls extension (this is Excell, I believe).

The body contains only a graphic representation of my company's name, with a slogan which is not mine.

However, the email comes from another domain, which has a name very similar to mine. Mine is mastercleaner.com, and the email came from (or apparently came from) mastercleaners.com.

I don't know if opening this email is safe, so I thought I'd ask the experts here.

Thanks,
General Tsao