There are quite a few options when it comes to UO emulators. World of Dreams is a POL shard (
http://www.polserver.com). POL is a highly configurable UO server program, but its not exactly easy to get started with. The WoD scripts are available for anyone who wants to use them. More information about them can be found on my website at
http://drocket.net/pol_stuff.html . In addition to the WoD scripts, there's also the main POL distro, which can be found at the main POL website.
In addition to POL, there's also RunUO and Sphere. I'm not very familiar with either of them, so if you would want to use them, you'd have to post any questions on their webboards.