To be able to play on Uldaris you can just download the LAUNCHER that will simply download the whole game ready for you, complete with all the needed patches.

Otherwise, you can also use any other Wow client (version 3.3.5a), just be sure to modify the realmlist like this:
SET realmList uldaris.net
You can find the realmlist.wtf file inside World of Warcraft – Wotlk/Data/enUS/ folder (enUS will change depending on your language).

You’ll also need to download the Patch-4.MPQ and put it inside World of Warcraft – Wotlk/Data/ folder, but be sure to remove any other patches from other private servers before launching the game (only patch.MPQ, patch-2.MPQ and patch-3.MPQ must be there). You don’t need to download any patch if you’re using the launcher.