there are no Linux viruses in the Live.
Proof of concept ones exist but due to the secure nature of the OS they can't easily run themselves ( they need to use social engineering at the very least) and unless the user is logged in as root ( teh super user) which is disabled by default in most ditros then they can't touch the OS files in any way.
Buffer overflows can exist to elevate privilages but again I've never heard of one being exploited in LIVE and the patch strategy of Linux is such that once identified teh time to fix is far quicker than Windows with its regular patch release date.
Its VERY easy to install nowadays. The only headache you may get is if you have some weird hardware that isn't supported but this is becoming a rarer event by teh day.
Ubuntu Home Page | Ubuntu is a good place to start.
Feel free to ask if you have any Qs