first have him decide how much of his hard disk he can spare to linux (min 20 gb recommended) if he does a lot of video, audio, or graphics intensive stuff, have him assign generously.
use the vista tool to shrink the partition as far as it will go - usually about half - and if more is required for linux, boot the livecd and continue to shrink from there.
decide on the partition arrangement for linux. if in doubt, assign the whole of the new partition and be done with it. format the new partition(s) to ext4 and install. if using the whole of the partition, the installer will offer to use it and will format automatically prior to writing the os to disk.
giving the full spec of the machine will help to determine what advice you get.