Well, here's an update on the original post. I haven't solved it yet, but I got a good suggestion which seems pretty obvious now. Even though I have a Dell mouse, it's such a generic one that MS Intellipoint will easily work with it. I just downloaded and installed it (selecting the basic "wheel mouse" as my hardware). This gives me nearly the same list of action options for each of the three buttons as Logitech's software does. Nearly. The only option thats missing, wouldn't you know it, is something like "Open start menu." There's even a choice for a keystroke, but if I try entering Ctrl+Esc, it opens the start menu and interupts the training.

It was also suggested to me that this feature was in an older version of Intellipoint, which seems even more odd to me. I would think that this thing I want to do is like the most Microsoft-centric thing I could imagine , but it doesn't appear possible.

*edit*
Well, I feel like a fool. I'm not sure why I thought it, but I just assumed that because I didn't have a Logitech mouse, naturally the Logitech software wouldn't work! Well I'm dumb It works just fine and now I've got the start menu coming up like I wanted it to. Duh!

Thanks for the help, folks.