You don't have to create a new partition unless you want to multi-boot your system, you can:Why do I have to make a new partition?
1) Boot from the LiveCD.
2) Boot from a USB device.
Run it under VMWare.How can I install it so that I can boot to Slackware and click on a Backtrack shortcut and run it from there?
Do a search there is lots of info on the forums about BT and VMWare. Though keep in mind that virtualizing will cost you some performance and compatibility.
On a related note if the difference between an operating system and application are a concept which you find confusing then there are a lot of things in BT that you will likely find confusing, therefore BT may not be a good distro for you.