The Inputs are L / R (L being Input 1, R being Input 2) in Stereo mode. You can just feed the XLR or 1/4 cables into the inputs on the bottom of the unit. HOWEVER this will generate drums on one side and vocals on the other. You are MUCH better off to use the Stereo Output on your Peavy for a board recording. The Zoom has 3 preset gains on those (H, M, L) so you can experiment to get best level OR it has a manual level setting for more precision if you wish.
If you want to have 4 channels at once (ie use the built ins AND the inputs) you will need to buy an H4n. The H4 WILL do 4 tracks but it is 2 at a time. IE lay 2 tracks, go back and lay two more.
If this is a "Live" situation you are MUCH better off just setting up two decent mics in the room and going straight into the XLR inputs on the Zoom.
If youu are trying to do a studio recording there are better units for that. See Zoom's site they make up to a 24 channel unit. If 4 is all you need the H4n will do nicely at $299, it even has a built in guitar tuner and lots of effects.