Yes you will need a partition to install Linux and NT on the same box. As for versions, I prefer RedHat but everyone has an opinion, usually biased by what they have used. To install it you will first need to split your disk, if you aren't familar with this I suggest getting Partition Magic. then boot off of the Linux boot floppy and follow the instructions. The only gotcha is being careful not to format or install over the NT partition. I would backup anything really important. It's really not that hard though.
Good luck
