| | Similar problem
I just upgraded from Cingular to T mobile and tried to put the T Mobile software several times without success (uninstalling the software for both desktop and handheld software).
Finally I uninstalled and deleted all folders on my hard drive referencing RIM (I had a problem with one subfolder, but I was able to move it and then it had no effect on the install). Once I did that, the install went perfectly according to thw directions that Seattle18 has on this forum.
So try not only uninstlalling but also deleting the RIM folders (both under their own folder and also under the common foloder) and then installing. I didn't lose a single name/phone number and my installed apps were still there.