I have the SMT1000I SmartUPS myself and it works wonderfully. Here is how you need to set it up...
1. Plug the UPS itself into the mains with the standard 3-pin UK plug as you have already done.
2. In the accessories bag you should have been given with the UPS are two mains leads which have a male kettle lead on one end and a female on the other. One of these should go direct into one of the 2x4 sets of plugs on the back of the UPS. The other end, of course, goes into the Mac Pro.
3. Do the same with the other lead and your monitor.
4. Do NOT connect any form of printer to the UPS - especially a laser printer - as they draw a high current when first turned on. This is mentioned explicitly in the UPS manual.
5. Connect the thin USB lead in the accessory bag to the UPS and a spare USB port on the back of your Mac Pro. This is a "handshake cable" that lets the UPS talk to the Mac and discuss things like when to do a controlled shut-down if the batteries are getting low. NOTE : this cable is technically optional but it would be a good idea to use it.
6. You do not need ANY software to use the UPS with your Mac - completely ignore all the install CDs and drivers etc. As soon as you connect that USB handshake cable, OS X immediately sees it and says "Aha - I detect a UPS so I had better display the UPS status icon on the top right menu bar."
7. If you want to connect low-current items such as cable modems, wifi routers and USB hubs to the UPS (especially those with power transformer blocks), you need to get yourself a standard british 4-way mains extension with a relatively short mains lead. Chop off the 3-pin UK plug from the end and replace it with the following item from Maplin...
http://www.maplin.co.uk/euro-line-plug-1360?C=73669 it is the female end of the kettle leads.
If you need any more info about setting up your SmartUPS 1000, feel free to send me a PM.
Daniel.