You can install it on any many PCs as you want. Ubuntu is all free.
Dual boot is the way to go. You will have two OSs to use.
This way you have Windows while learning Ubuntu at your own pace.
All you need is 20GB for an Ubuntu partition and you will be on your way to becoming M$ & Apple FREE.....
Just downloaded and installed the latest version Ubuntu 9.10 Karmic Koala.
So far I like what they did. Boots up in < 1 minute.