So I have this punk/alternative song that I've been working on.

My equipment is all pretty good quality. I'm playing on a Schecter with SD/59 pick ups, a Fender amp, recording with a Shure Beta 57a mic, and using an m-audio interface.

I did all the drum and bass on the computer so it sounds great.

As for the guitar recordings, the quality is okay. It's comparable to say, the Dude Ranch album by blink 182. So it's not excellent quality.

I have the rhythm guitar track down, and it sounds pretty full and loud. But I also have the Lead guitar (riffs) to put in there.

Should I pan the rhythm to one side and pan the lead guitar to the other side?
or should I have two rhythm guitars panned left and right and record the lead guitar to one side?

somebody please help me out.
I usually record 2 rhythm guitars to the left and right then the lead in the center. But I'm no expert at recording I;m sure someone with better experience will answer :P
^this. Or rhythms hard left/right and double track leads hard left/right.

It worries me though that you say rhythm guitar track rather than tracks. You should be recording each rhythm part twice and panning them 100% l/r.
It's pretty much a matter of personal (or the band)'s preference and of course style of music. I like having quite a big guitar sound so I often re-record parts quite a lot with various different guitar/amp and mic combos but unless you know what you're doing in terms of actual recording and EQing further down the line it can get very messy and muddy.

An easy way to get this effect with lead parts is re-amping. Playing a lead guitar part over and over on top of each other can end up sounding messy unless you're playing is absolutely perfect and your guitar always stays exactly in tune etc so the way I do it is to split the signal while you're playing, one into a DI and the other into the amp you're recording. I mainly use the amp for monitoring at this stage to be honest to get the guitarist to get the feel of the part but if it sounds good keep it. Next send the DI'd (Or dry) sound from the out into another amp, and record that amp and so on and so forth.

Mind you, this only works truly well with very good gear. If you have a cheap interface and a low level computer these will colour the sound, and usually in a negative way.