Hi Mac

You can move a folder from C Drive to D Drive by clicking on C Drive > Open the Users Folder>Right click on Your Name Folder and choose open> Right click on a folder (say My documents) choose properties. On the tabs choose location and change C Drive to D Drive and click on move.

You can also do as suggested at: http://answers.microsoft.com/en-us/windows/forum/windows_7-performance/move-the-my-documents-folder-to-another-drive/a41eaabb-2c5b-4502-85ba-fd49a007fd82

I agree with Ron Barker.  Relocating the user folders is a much better solution than merging the two disks.  The procedure is both quick & reliable but you should make a file backup of your user files within your C:\Users\YourUserName folders first anyway.

I started the procedure by creating a D:\Documents folder & moving my data files into it.  Then I set the Location tab in C:\Users\YourUserName\Documents to point to D:\Documents.  Then I set the access permissions for D:\Documents by right-clicking on it & selecting Share with, Specific people or right-clicking on it & selecting Properties then the Sharing tab.  Then I repeated the procedure for

Music D:\Documents\Music,

Pictures D:\Documents\Pictures,

Videos D:\Documents\Videos,

Favorites D:\SystemSettings*\Favorites,

Links D:\SystemSettings*\Links,

Searches D:\SystemSettings*\Searches.

[* It just suited my backup plan to separate these settings into a different folder group.]

The separation of your data files from your OS & its applications does not just free up space, it also allows you to make regular system images of the C:\ drive that are almost certainly going to be 40GB or smaller [and only take 20 minutes to do]. 

This would give you excellent disaster recovery capabilities as your response to serious system corruption could then simply be to boot from a System repair disk or Windows 7 installation USB/DVD and restore that image, i.e. restore the system drive, to exactly what was on it at the time the image was made.  This restoration also only takes about 20 minutes.

I did this a couple of years ago and would never configure my system any other way now.  I had previously only regarded system images as a tool that IT departments used.  I now make regular system images on external drives and can therefore recover from disasters reliably & quickly.  For example, I am just about to investigate the Registry settings that are interfering with one of my System tray, Notification area icons and I will be able to do that investigation because I know that I will be able to get back to square one even if it all goes horribly wrong.

With separate system & datafile drives, you would continue to make straightforward file backups of your own files on D:\ using Windows Backup or any of the other utilities available for that task.