I am a Ubuntu user, and as much as I like Linux - I must warn you that you will suffer with Linux only. Dual-booting is a must for a home user and it isn't rocket science. You just have to select which OS you want to boot at the start...
There are many things that you just can't do with Ubuntu that you can do with Windows and WINE doesn't always help - think about video editing. Programs available for Linux sucks dick compared to windows.
Anyway, I have an Acer eMachines Zsomething - 3GB ram, 2.13 or something GHz processor, 256 integrated video card.
Not very fancy but is very nice and does the job for me - I don't play games or watch HD movies at all, so it's fine for video editing, coding etc.