The multiplayer option is a seperate program, you have to start that one in order to get to the multiplayer screen. From the launcher select the multiplayer option, or from your installation folder just run the jk2mp.exe file. There should be several 1.02 servers available (at least there was last time I checked).
However given that you bought the game recently it's probably patched all the way up already - if it says 1.03 on the singleplayer version, it is fully patched (1.04 is for the MP version).
"Words are deeds." - Wittgenstein