You can use Disk Management in Vista to Shrink the C: drive into two
partitions and Create a new drive letter with the new second partition.
This tutorial will show you how.
I have a PC pre-installed Vista .by using Disk Management i made two
partitions already. but thing is my c drive was 200 gb. i have splited 100 gb
each. bt i want 40 gb in my c drive . how it is possible.