I'm looking at putting a 2002 ser tranny in my b13, how do I know if it has teh locking diff?

You need a B15 2.0 SE Transmission for a direct swap, but the using B15 SER transmission is possible with a VET bellhousing and some other mods.

so does the 02 2.0 ser tranny have locking diff?

Some did. Look at these two threads:

http://www.sr20-forum.com/howtos/725-lsd-vs-non-lsd-transmission-axle-comparison-pics.html

http://www.sr20forum.com/general-sr20/158084-side-side-b15-vs-b13-tranny-pics.html