Fedora/Mandrake/SuSE (Redhat base) all offer disk resizing (Fat/Fat32/NTFS/etc...) tool. Mepis/Ubuntu (Debian base) offer Qparted to resize your disk as well.
The above distros are mentioned becasue they are relatively easy to intall and have load of bundled softwwares that came on the disk. SuSE can be download @ 3.1GB DVD, that included over 1000 application on it and more can befound on Novell site or 3rd party sites.
Download the user or admin guide of the distro that you want to try out & read the instruction on dual boot. Or, backup an image of your hdd, then reboot with one of the above linux distro and follow the wizzard to intall a dualboot system.