How can I join any server havin client not from site.

Hi!
Can anyone help me? I can't get any information how can I join when I downloaded client from another site. I need only realmist or what?


Edit:
Sorry guys I already found that. So I ask something else. If I have Mist of Pandaria expansion I can play on Wrath Of The Lich King expansion?

Edit II:
The thing is I can't join MoP from another client. I use client from .................. which have custom launcher I think. Any advice how to play on warmane? I changed realmist and deleted cache folder but when I try to log in it says I have to convert account on battlenet.

Generally other server clients tend to be compatible as long as the client version is the same. That is 5.4.8 for MoP and 3.3.5a for WOTLK.
When it comes to the realmlist:
WOTLK - Data\enUS\realmlist.wtf
MoP - Config\realmlist.wtf
Make sure the file were you are making the changes is the right one.

For MoP I got some not official launcher I think becouse its called "serer name launcher". Worst is this that I just downloaded WOTLK and can't create character on Icecrown, I got "error character creation". What's the problem?

Only on Drenei Shaman I got that error. I wanted to have shaman on Alliance :(