I'm adding some dialog to the game, but have been having a little trouble. I want an NPC to say something new when I have a specific party member with me, but for the life of me can't figure out how to make that happen. What is the script that I should use?

Use one of the c_con_*pm scripts as a condition for the dialog branch. The names are:

c_con_attonpm
c_con_baodurpm
c_con_disciplepm
c_con_g0t0pm
c_con_handmaidpm
c_con_hanharrpm
c_con_hk47pm
c_con_kreiapm
c_con_mandpm
c_con_mirapm
c_con_t3m4pm
c_con_visaspm

Not only do they check if the character in question is in the current party, they also check if the character is close enough to the player.

Thanks. I'm actually using KOTOR I, will it make a difference if I just put in a different name?

For KOTOR I, the scripts begin with the letter "k":

k_con_bastpm
k_con_canderpm
k_con_carthpm
k_con_hk47pm
k_con_joleepm
k_con_juhanipm
k_con_missionpm
k_con_t3m3pm
k_con_zaalpm

(Notice that "t3m3" is actually T3-M4.)
There is also a set of scripts that check if a character is not in the party, they end with "npm": k_con_bastnpm etc. Also, since KOTOR I only allows one condition per branch, you may wish to extract the scripts' sources (NSS files) from scripts.bif and insert them into your own scripts if you need additional conditions to be checked.

Thanks a lot. I thought that was it, but what I typed was 'k_con_t3m4pm'.