kung may amp ka na, pwede naman isaksak mo yung guitar with effects sa amp, tapos itapat mo yung mic sa amp (hanapin mo kung san pinaka ok yung tunog --- improvise nalang if you don't have a mic stand, basta wag mong ibitin yung mic sa amp, dapat nakatapat or slightly angled from the cone --- yung distance depende narin sayo --- pwedeng cm's or pwedeng inches or feet away from the amp). after that saksak mo yung mic sa mic input ng sound card and then record the mic'd signals. this is how i do it in the studio. if you find that doing it this way produces unwanted distortion, pwede mo ibaba yung volume ng amp, or ng mic in, as long as when you record the input is just below the red meter.
feedback can be recorded using an amp. i don't know if this pc simulation will work: produce a sine wave with a frequency same as the one you get from amp feedback (experiment nalang) and then pass it through an amp simulator plug-in , fade it in, and cut it when the guitar parts begin. komplikado. better kung sa amp nalang, natural pa.