i have the same sound card sort of, i have an audigy 5.1 with the front panel interface. i use cakewalk sonar 2.0XL, it's really user friendly, and sounds good, plus tons of effects and plug ins to dick with.
here's how i have my humble home studio set up. i usually mic up my amp, then run it thru an old 4-track for a pre-amp of sorts, from there i run it into an alesis midiverb 4, then to the front interface of my sound card (line in, because the 4-track sends a line level output).
mic -> 4-track -> alesis -> soundcard.
if you were going to plug in direct, i recomend to do it this way.
guitar -> processor -> pre-amp -> sound card.
In the recording software you will have a virtual mixing board, you can level everything there.
if you don't have a pre amp, then you could just use the line out of your processor straight into your line in port of your interface, and adjust the level in the program, keep in mind it doesn't sound very good that way, unless your box was made for direct plug in. there are cakewalk plug-ins (programs that run with cakewalk for certain effects, like cab sim, or amp modeling) that can adjust for this set up and simulate a more warm signal. i have a plug-in called "amp farm" it is basicly an amp modeler, but it also has effects that can make a sterile signal sound like it is run thru an amp first. pretty cool, but requires some tweaking.
you can download lots of free recording software, just do a google search for them.
also you could always get one of those guitar-port things by line6. those are ok for direct recording.