Getting ServUO is easy. The hard part is deciding which is best for your needs. For simple cases, you'll probably just want to grab the Shard-In-A-Box download below. If you would like to easily add updates from the public ServUO repository, then you shouldn't download via the link below.
What is a Shard-In-A-Box you ask? Simple, it's just a pre-compiled version of ServUO. These pre-compiled downloads (the ones you see below) are only updated at major release points of the project. It's perfect if all you need is a simple shard for you and your friends. However, it's probably not the best thing to use if you plan to keep your server in-sync when it comes to updates from ServUO.