Bought Logitech USB microphone for use with Mac G5 using 10.4.7 but when I try to record sound on SnapZ Pro X, no sound is availalbe in the QuickTime file .

Tried exactly the same thing with an older G4 which uses a non-USB mike and it worked find. Sound quality was so poor I decided to buy the new mike.

Have you selected that USB mic as the input source in the Sound System Preferences pane? Is the gain high enough in the Sound System Preferences pane?
Did you make sure you checked the Microphone track checkbox when you make the size selection.
In the save screen after recording, did you make sure you have checked the Include microphone track checkbox?

Hello-
halprinp is on the right track.

Be sure that mic is set as the Input source in the Sound pane of your System Preferences.

Then in the movie settings palette of SP X before recording the movie, be sure the mic track option is checked, and then uncheck the auto mic input gain right beneath that option.

After that SP X should be able to record from it at the level set in the System Preferences.