Ubuntu/Kubuntu should work great on any computer with 512MB ram or more.
If you got less than 512MB of ram you should try Xubuntu, which uses the XFCE desktop that takes up far less RAM.
Linux is the best OS to use due to it's very high level or security and the pile of free software / games for it. It's also easy to use but at some point sooner or later you will need to learn how to use the terminal and such.
Good Luck !
