Well first save your data :P.
after that usually it's best to have a book around you (about ubuntu).
You can get one from www.knowfree.net
The book is not only for the installation procedure (it's a very simple procedure) but also for installing packages, setting up the desktop, etc etc.
You can do very well without the book ..but will save you from posting very soon on this forum :P
Ubuntu will be very good for you...lots of packages easy to install by Synaptic Package manager, simple and powerful Administration and Preferences tools, good hardware support, very very good support forum and documentation.