This is the Adobe Reader forum; you may get better answers in the Acrobat forums.
However, are you able to install Acrobat 5 on Windows 7? If so, you may need to run it in Windows XP or 2000 compatibility mode.
Acrobat 5 is not compatible with Windows 7. You may have some luck as mentioned with compatibility mode, but then you will leave yourself open to the legion of exploits that have not been patched in your ancient software. If you only want to open attachments use Adobe Reader:
I was successful in installing AA5 in Win7 Starter as a test. It works except that I changed the printer port to file (AcroTray or the Distiller Assistant of AA5 does not work in Win7). You can open the files that are created in Distiller to create PDFs. You may be able to use watched folders to automate the process to some degree.
I suspect that your question is more of having problems reading PDF files in AA5. That is a different issue. It is not a Win7 compatibility issue, but one of needing a newer PDF viewer. I have AA5 on one XP machine that I use Reader X on for seeing the newer files. I do have to deal with some conflicts between AA5 and ARX, but I can deal with that (many folks lose there minds on that).
There is one other option that might be a major problem. Many folks are getting Win7 on 64-bit machines. In that case, you will have to be sure AA5 runs in 32-bit compatibility.
At least that should give you some ideas of what might work. If a 64-bit machine, you may definitely have a problem -- I never tested that combination.