Personaly i have no idea how that game operates, but i would assume you could add that ip to your fav’s and then connect to it. I have seen 5 people at a time in it. UT is mostly a team based game from my knowledge, and we will will use that server for our next lan provided that we keep the box were currently on.
You may also want to consider using HLSW http://www.hlsw.org and adding the ip in it and pressing the connect button. It should send you directly into it
to add an IP address to your favorites list, go to the favorites list in your server browser (in UT2004), right click, and click ‘add to favorites’. To open an IP address, go to any tab in your server browser (in UT2004), right click, and click ‘open IP address’