Different Excel Releases

Office11 is indeed Office 2003. However, as far as I'm aware, Office 2007 takes control over office files if it's installed. You won't be able to open them in Office 2003 by double clicking the file if you have Office 2007 installed, because they're the same program. But Office 2007 is the most recent, so Windows uses that.

Opening Office 2003, then using File -> Open should work.

As a training company, we faced this problem when Office 2007 was released: half of our delegates wanted training in Office 2003, and more and more delegates required training in Office 2007. The obvious solution is to have both installed on the computer. During our tests, we found that we experienced problems with this, one of the main ones being the one you mention in your original post.

Therefore, we now have two partitions on our machines with a separate Windows operating system installed on both partitions. One partition has Office 2003 installed, the other has Office 2007, thus allowing us to train our delegates in either version.

Microsoft does not recommend having more than one Office version installed. But they do give advice for people who require it. See this article for more information Graham:
http://support.microsoft.com/kb/928091

Regards, Rich