BleepingComputer.com: I Cannot Shrink The Operating System Partition Very Much

I have just bought a Dell PC and it came with 3 partitions:
FAT 16 - Dell Utilities
(NTFS) C: Operating System - Vista Home Premium
(NTFS) D: Recovery Partition containing Dell's PCRestore and an ImageX image of the Operating System
I would like to reduce the C partition from approx 240GB to 35GB, so that I can insert a new partition in the remaining space. When I go into Disk Management and try to shrink the partition, I am only allowed to shrink it to 110GB.
Can anyone explain the reason why this might be?
Thanks

vista has all kinds of hidden files and reserved space that you can't see, I had to disable a memory dump? can't remember where i found it and then disable system restore(it was a new computer) to get my system partition down to 35 gigs, that's as small as I would go tho, and you had better watch what you install then

on your right now vista is reserving 40 gigs for system restore, that's silly

There are plenty of laptops being sold with 80GB hard drives. How is Vista managing with that? Microsoft say the following in their system requirements for Vista Home Premium: "40 GB hard drive with at least 15 GB of available space". I mean, that is a strange concept. Do they need 40GB or 15GB? ....and how does Vista manage with such a small amount of space when compared with the 110GB that it seems to want from me?

vista reserves 15% for restore, 15% of 40 or 15% of 250

and then there's the memory dump, swap file and coffeebreak, afternoon tea break parts whatever

If I can remember hibernate is one of the first things i turn off with XP never worked right anyway, for notebook clients I ask first