Acrobat Standard 8 and Reader 7?

I've read posts here about installing Reader 8 and Acrobat 7 (and the dangers therein), but I haven't found anything about the opposite.

Here's my problem: I have an application that works with Acrobat Reader 7 and Acrobat 7. When you click a button in the application, it's supposed to open the PDF (and, in some cases, jump to a named destination).

With Acrobat 8 (Reader or Standard) installed, it will not open the PDF. Instead, it opens Reader and then gives me a "file not found" error (multiple times).

Ideally, I'd like to have the application work (without being modified) with Reader 8. Any idea why something that would work in 7 would give a "file not found" error in 8?

If this is not possible, then I'd like to know if I can have Acrobat 8 and Reader 7 installed at the same time, such that Reader 7 is always used to open PDFs (but 8 is used to create PDFs)? 8 is already installed (and I'd prefer not to have to uninstall and reinstall if at all possible), but Reader 7 won't even install (saying that there's a "more functional version already installed.") If I have to reinstall 8, so be it. But can I then install Reader 7, re-install Acrobat 8, and then do something to set the machine to do what I want?

Thanks!