Follow the simple steps below:
- Click on Start in Vista.
- Go to Control Pannel (Follow steps pre-fixed 'A' for "Control Panel Home view" / 'B' for "Classic View").
- A: Click "System And Maintenance" (in green).
- B: Click Administrative Tools (the one with a big gear icon).
- A: Under Administrative Tools, click "Create and format disk partitions" (If a UAC prompt apears, click continue).
- B: Click "Computer management" (If a UAC prompt apears, click continue), Next click "Storage", then "Disk Management".
- On the list provided, right-click the letter drive you want to rid yourself off (say D:) and choose the option "Delete Volume".
- If you have done it right, a black area should appear within your entire disk space.
- Finally, right-click your drive you want to add the space to (say C:) and choose "Extend Volume" (by default, the wizard will choose ALL unallocated space to add to your Vista partition, but you can change that if you'd like.)