Sounds like you're halfway there. To present two stimuli at the same time, you have to have two parameters set zero: the Time column of the first stim, and the "Clear" value of the second. (Clear is the third number of the ordered triple in the Loc column.) Check your "Clear" setting. If its value is set to 1, you've been telling DirectRT to clear the previous screen. Change it to 0 and you should be all set.

Good luck.

-M