Ubuntu installation

I have just recently reformatted my pc and reinstalled the pre-installed version of vista home premium. I have 2 partitions, one for vista and one 40 gbs dedicated to Ubuntu. The second partition is in ntfs format. When I insert the live cd and restart my pc, i am given the option to install Ubuntu on the desktop. So i press install, followed the steps but when i get to the partition manager i don't know what to do. do i just select the second partition for ubuntu and what's this swap space and other stuff? the second problem is that when i do the GRUB won't install and gives an error like hd0 failed. this is a fatal error. I am actually new to dual booting and i would love help on this matter.