Use any Desktop Environment/Window Manager you like, 512 MB is enough.
GRUB is good enough boot loader to dual boot with windows and it comes by defualt in ubuntu.
For partitioning purposes, IMO, fdisk which is used by linux distros is the best around. But, yeah it's rather a sharp tool, if you mess around much with no knowledge then you can loose information, but if you are just careful enough, there will be surely no problem in partitioning.
And don't forget swap partition of 750MB to 1GB.