For XP system, you need to use other partition software to adjust, such as PM8
Now, you are a Vista system, and you can use the built-in functions of the system.
You are looking for the right person. I just used this method to allocate some space for disk C as disk D!
Right click "My Computer" and click "Manage"
The "Computer Management" operation interface pops up
Click "Disk Management", and after a few seconds, the status of each disk and partition in your computer will be displayed.
In the "Volume" column, right-click on disk C and click "Compress Volume"
In a few seconds, pop up
Compress C
There is "Input compressed space (MB)" on it. This is the maximum available compressed space. You can't use the maximum value because you want to leave some space for disk C. Click the descending sign (triangle) on the right to make it smaller, such as 5566 (the unit is M, that is, 5.5G)
Then, click Compress. After a while, you can see that disk C has a corresponding amount of unused space. You can create a new partition