in this circuit here: http://electroschematics.com/220/12v-dc-220v-ac-converter/

could i substitute a couple IGBTs for the Darlingtons to beef it up a little? i have a couple SKM200GAL173D's laying around. data sheet is here:

http://pdf1.alldatasheet.com/datasheet-pdf/view/126776/SEMIKRON/SKM200GAL173D.html

 

Im thinking it will work, but would be nice if someone could verify for me. i just need help calculating the gate resistor

 

It likely will work. You can just use the same resistors (or none) for the gate since an IGBT draws no gate current.