hi
case 1:
using normal mode(look for a icon with "2 faces"),after compilation just before u give burn look for a check box sayin add files to be added later(multisesion);put a check mark and proceed burn.
case 2:
Using expert mode(click the abv mentioned icon so faces wear specs),after compilation give burn, and u reach to another window where u can see a lot of options, including multisession.
krive.