Well, my experience of trying to sniff or pentest under Vista is null.  You are going to need to be able to put your NIC into permiscous mode or monitor mode.  Cain and Able can do that if your NIC supports it.  Not sure if C&A is supported under Vista though, and I don't want to go look at the moment.  You can also packet capture with either Wireshark or Kismet.  Just do a search on insecure.org of wireless sniffers and you'll see what the most popular ones are.  If you want to really get into learning sniffing, or pentesting in general, I would suggest a different OS than Vista... preferably Linux, but definately not Vista.  All you will be able to capture is what traffic they are sending out, or possibly recieving on their computer, not specifically what they are viewing unless you open a connection to their computer with a remote desktop or vnc type connection via an exploit.  Or... go manually to whatever pages they are on.  Aircrack is a program that cracks WEP and WPA AP's after it's been able to sniff out an encrypted key from the 'ether'. 

You can use a vmware or other virtual box setup of Linux.  Or, many distros don't even need to be installed to just play around with.  You just boot off of their cds and you can play around with them and get used to using them.  Ubuntu is a good distro for someone new to Linux in general.  And I suggest it as the first distro to 'use' for everyday functions.  BackTrack is great for pentesting, but that is its entire focus.

And as always mitchell07, google is your friend.  It will clue you into more resources than you could want, and generally agregates your search to what you are looking for.... though not always.  In the case of Ubuntu and BackTrack though, it would take you right ot their home pages I'm sure.  You may as well use this sites version fo BackTrack though, it's pretty nifty.

Generally if you boot off a linux cd, or a Linux partition of your harddrive... you can almost always get to the Winblows files.  All Linux Distro's I've played with recognize NTFS and FAT partitions.  Infact, Knoppix cd's were my first intro to Linux.  Using them to recover data off corrupted Winblows parititions.  As for your question about using Ubuntu to access BackTrack... well I honestly wouldn't probably stick both of them on a pc.  If you plan to dual boot, I would go XP and Ubuntu.  Just download/install the programs you like from the BackTrack distro on your Ubuntu partition.  Or, to get into Linux you can just play around with BackTrack by booting off the CD.