So far i haven't seen that *. msi install file that needs password for installation .
Most of the time is used InstallShield with greyed OK button , and when it is ungreyed (or correct password is entered) , msi installer starts (you can see this with looking \temp folder).
Try with bp like "lstrcmpA" and similar .
However have you tryed with some msi extractors like : MsiEx 0.2 [tulipfan] (hxxp://www.wasm.ru/all.php?mode=tool) ?
Works fine for me
(after you have *.msi file from \temp of course)