How to format my system partition

Hey guys,
I want to format my partition, but when I try through

Computer>rightmouseclick > Manage > Disk control

it says I cannot.
A quick sketch of my situation:

I’ve got a Acer Aspire 7720G with 2 160GB HDDs
– C:\67gb – Installed Windows 7 on it manually. This is a primair partition and perfectly fine. – D:\67gb – Has currently Vista installed on it. Computemanagement says this is the system partition, even though I don’t use it.This has come together when I bought this laptop (Although I reinstalled the OS by downloaded OS) . This is also a primair partition and is perfectly fine.
– E:\147gb – This one is also a primair partition and works perfectly fine. This partition is mainly my Data partition. No OS installed.

So now the thing is: I installed Windows 7 and it works really great. So much better than Vista, even though it ran perfectly smooth. But to retain some HDD space I thought I format the VISTA partition. This I cannot do.
My question: How can I format the partition or do you recommend me not to do this, but you can give me an alternative?
Also: Does formatting the old partition, which obviously holds some virusses which makes it slower then it was before, makes my other partition, which I mainly use with W7, faster?
Thanks in advance.
Ps: All information or questions you have regarding solving this issue: Please post them.
Answer #1
use a partition manager and you should be able to do it
http://www.google.com?t=1084974&highlight=
also if you aren’t admin that may be the problem
also formatting one partition wont affect the other
it’s best to think of each partition as its own separate harddrive
Answer #2
use a partition manager and you should be able to do it
http://www.google.com?t=1084974&highlight=
also if you aren't admin that may be the problem
also formatting one partition wont affect the other
it's best to think of each partition as its own separate harddrive
Hey, thanks very much. I will try asap. Tho I hope some other people can comment on my question so I will really be sure.
Still my question: Why is the other partition (D:\) The system partition?