I hit a problem when trying to get both Acrobat Reader 7 and 4 available under the WinXP “Open With” right-click menu. When ever I’d point the WinXP dialog to Acrobat 4 it would just use Acrobat 7 instead. The problem seems to be caused by both executables having the same name even though they are in different paths.
The solution is to copy the Acrobat 4 executable AcroRd32.exe and rename it, I named it AcroRd4.exe. Now the “Open With” selection works and I can choose either version to open a PDF.
On the other WinXP PC that I use regularly this problem didn’t happen. The only major difference between the PC’s is that the one that it worked on had Acrobat Reader 7 and the full Acrobat 7 program both installed.