I don't have a whole lot of direct experience with Linux per se, but it is a 'Unix' flavor so it is not a whole lot different than other Unix flavors. Unix can be much more secure than XP just in the fact that it is Unix. The operating system provides quite a lot of security right 'out-of-the-box,' and the system is far more stable than XP with benefits of protected memory so that when a program crashes, it doesn't take the OS with it. There isn't a whole lot of software written for Linux yet though that is slowly changing so that can be one count against it. Luckily, Macintosh based its new OS on BSD Unix so security updates come from them when a 'hole' is discovered. With Linux, you'll have to keep up to date yourself and apply patches yourself unless they've created an automatic software update like Apple did for OS X.