What is the way to create a staff holding percussive sounds in the same sheet containing the melody?
Create a new staff as always. Set it to Channel 10 (Staff Properties | Midi tab). Each note will now be a different instrument in the drum kit. See drumref.nwc in your Samples folder for which notes correspond to which instruments.
On some sound cards and synths you can select different drum kits by changing the instrument patch; example - the "Acoustic Bass" patch gives a different kit than the "Grand Piano" patch. Consult your soundcard/synth's manual for the available kits.