After the .dll replacement, R14 would open but I was getting two error messages. On opening, I would get one message about being unable to modify the registry and a suggestion to open REGEDIT (no suggestion from Vista on what to do in REGEDIT though).
On closing R14, I would get an error about not being able to write or save configuration.
I looked for what could be considered a registry file. "acadaut.reg" was what I found that looked like a good option in the "c:\program files\mechanical" folder, which is where all of the R14 support files tend to be on my machine. So I right-clicked on the file, selected 'properties', went to the 'security' tab, and edited the permissions so that 'write' access was allowed. I actually, granted 'full access' because I didn't notice 'write' as it's own selection, but that was probably more than is needed. I then looked for what would be a configuration file and found "acad14.cfg". I went through the same permissions update with it. During all this, I'd make a change and then try out R14, make another change, try out R14 again. After/During this, I felt the need to go and run REGEDIT, right click on each major folder, and update the permissions to allow writing there too. Now I have a working R14 on Vista 64-bit.
My version of R14 does include mechanical desktop, however I mainly use the AutoCAD program. Also, AutoCAD seems to prefer being installed in the Program Files area, not the Program Files (x86) directory. Hope this helps out.