i have problems with restoring my iphone 3gs on my pc with mac osx 10.5

i bougth UDID registration an i tried to restore my iphone with the os4 beta but it doesnt work. on itunes the bar is at ca. 93% and on the iphone its 3/4. it doesnt finish.
than i tried to restore it with 3.1.3 and got the same problem. after that i booted windows(i have dualboot w7 and macosx) and restoring 3.1.3 worked. it as far as i know i cant install the os4 beta with windows right?

so maybe someone knows what it could be?

best regards