I have seen several threads about installation problems with DM and Vista. Here is how I got mine to work.

Environment

Vista Home Premium (patched to date)
Desktop Manager with SP2
BB Curve

1. Make sure that User Access Control (UAC) is enabled for the user account on which you want to install.

2. Run the "blackberry desktop software.msi" to install the DM app. (Just as a side note I did not install the roxio portion of the software, should not matter though)

3. Once I disabled the UAC and rebooted the PC.

4. Right click the Desktop Manager shortcut and select properties. On the shortcut tab select the advanced button then check the box to "Run As Administrator".

Hope this helps anyone who is having issues with the DM install.