What is your opinion of installing SMS secondary sites (management point and deployment point) on a domain controller that is also running Exchange 5.5? Is this something that you have heard of anyone doing successfully? Is this something you would recommend? Or would I be better off putting a desktop at the location and running the secondary site from it? I would appreciate any advice you can give.
I've never heard of this combination before, and checking with two of my colleagues puts even more doubt on the picture. Exchange 5.5 is not regarded as all that stable, and the SMS system can be a fairly heavy load as well. I'm not concerned about the domain controller (I'm assuming this is NT 4.0 since you mentioned Exchange 5.5), since that is a relatively light process, load-wise.
I'd recommend that you go with the separate desktop system with server software on it, since I strongly suspect that SMS will not even install on a workstation, although I've never tried.