Problem shrinking a partition

Hi,
I’m trying to create a dual-boot for Windows 7. But in order to do so, I had to shrink of my partitions in order to create a new one. The problem is that I can’t shrink my partition (300gb, 250gb free) with more than 237mb. I’m using the windows tool in windows vista. Any thought on why this is happening and/or a solution for it. Can I use gparted instead?
Greetings,

Daan

Haven’t tried the Vista partiton tool, but Gparted works just fine.

Here’s a link to a little guide if you need some help: