if you are used to windows, is that with linux you can have different "interfaces" - think of it as sort of like different "tops" on the OS. You can have multiple ones on the same machine and change them by just logging off and logging back on with a different interface.
Ubuntu makes it really easy to install linux on a windows pc. You wouldn't have to delete xp. You would install it along side windows and when you boot up you choose which one you want - windows or ubuntu - for that session. They've made the installation really easy.
Ubuntu comes "standard" with an interface called "unity." It probably would seem a little more "like a mac" than "like a windows" imho, but it is easy to learn. The current version of Ubuntu is 12.10; if you go back to the last version from 6 months ago, version 12.4, you can choose a different interface called "unity 2d" which is uses less resources than the default unity. I'm using it right now on a 6 year old laptop with one gig of ram and a pentium dual core.
In addition to xubuntu, there is another interface called lubuntu which is really easy to use. It will seem a lot like windows xp. A little more customizable. It flies on this laptop.
Basically, you can install ubuntu alongside the windows (I would get version 12.4) and then go to the software center in unity and download other interfaces and try them on and see what you like. It may not be obvious at first, but if you play around with them you will find they are much more customizable than xp, and they will be much more stable.