- Ubuntu is completely free.
- Ubuntu has a Mac-like interface.
- Viruses are essentially unheard of on Ubuntu systems.
- Ubuntu has thousands of free applications written for it.
- Ubuntu makes it hard to hurt yourself if you don't know what you're doing.
If Ubuntu is so great, why doesn't everyone use it? Well for one thing, there are a great many idiots out there who believe that if something costs more, it must be worth more. This is simply not the case; there are a number of free alternatives for many things that are as good or better than the leading pay-for equivalents. Also, people are simply afraid of what they're not familiar with. They wrongly believe that since Linux is popular with nerds, it must be difficult to use.
Where do you get a computer with Ubuntu on it? For a while now, Dell has been selling a number of systems with Ubuntu as the operating system. They of course pass down the savings directly to you. There are other lesser known companies that sell Ubuntu systems, though personally I would go with a well known company.