HDD / Partition reorganization / IM-possible !?

[SYNass IT Ubuntu / Linux]

Hello Ubuntu Experts and Users
Hope it's not off topic here because it's more the WIN part of the
system !

After swapping / upgrading to a bigger HDD with the originally
recovered 
WIN XP Pro, we want to install Ubuntu 7.10 to that system too !!

The new HDD is 80GB and the WIN partition (C:) shall be shrunk to ca
25GB 
to leave a fair rest for a shared D: FAT 32 partition and some more then
for 
the Ubuntu installation !!!

Unfortunately the C: partition gets shrunk to 40 GB and 
does not go even lower as wanted !! ;-(

What can or must I do to get it done properly ?
Tools already used to shrink were: Partition Magic 8.x and DFSee !!

Will a Linux / Ubuntu tool from its CD do the needed task and 
how do I as Ubuntu newbie ???

Your advice and (cookbook) guidance is very appreciated. ;-)
TIA for your help, cheers, svobi