This is a followup question for the following thread:
https://boinc.berkeley.edu/forum_thread.php?id=12712

Exit BOINC (BOINC Manager->File->Exit BOINC Manager->check "Stop running tasks when exiting the BOINC Manager"->OK)
Navigate to your BOINC Data directory (default in Windows a hidden directory at C:\Programdata\BOINC), then go up one folder so you can copy the BOINC folder.
Copy the BOINC folder to a folder on your D: drive (e.g. D:\BOINC)
Uninstall BOINC.
Reinstall BOINC.
In the third screen of the installer, click Advanced.
Change the path for the Data Directory from C:\Programdata\BOINC to D:\BOINC (or wherever you copied the directory to).
Continue installing BOINC.
Start BOINC Manager (Start->All Programs->BOINC->BOINC Manager)

We do it this way and not via the registry to make sure that all permissions on the new BOINC folder are set correctly.
If you miss the installer of BOINC, you can get 7.14.2 from here.
If you have trouble uninstalling or reinstalling BOINC, use the Microsoft Windows Program Uninstaller.

Does this work if there are tasks in progress that you want to retain? I need to know this because I have a project (climateprediction.net) where the upload of finished tasks is blocked because the project's server is having problems, and it's taking quite a while for them to fix it.

System: Windows 7 Pro x64
Boinc: 7.14.2 (not installed as a service)
Projects:
LHC@home
climateprediction.net

Yes, it does. Everything that BOINC needs to store is contained in that single folder and its sub-folders, including all the results so far for a task in progress and completed tasks.

The only thing I'd suggest for a project like CPDN is to take it slowly - especially at the first step, "Stop running tasks when exiting the BOINC Manager". CPDN can take a little time to flush everything to disk and shut down the applications in an orderly fashion.

Great! Thank you for a blazingly fast reply!