Go to a regular User Voice (one that you don't need). Initialize it so you have clean voice to start with. Press File and select waveform as the type of file to load. Select the samples that you would like to load, and load them to different keys by using the keybank parameter. This will map the different samples across the keyboard.

When you are done you will have a regular user voice with your snares and kicks laid out across the keyboard. Now you want to turn this into a drum voice.

Go to Sample Mode by pressing sample and then press Job. Jobs are macro editing functions. Under F3 Other, there is a job called Convert to Drum Voice. This will take your waveform and convert it into a Drum Kit voice automatically. You probably want to do this so you can have a separate amp and filter setting for each drum.