Quicktime to mpeg4: where's my audio gone??

Been trying to convert some Quicktime video files to install as mpeg4 files on my shiny new 30gb Video iPod, as any attempt to load the original Quicktime file results in a message stating that it, "cannot be played on this iPod." However, when I utilise the "Convert Selection For iPod" utility in iTunes, my iPod index allows me to import the file successfully without any warning/failure messages. When I consequently access the file on the iPod - and iTunes, for that matter - the video content plays back fine, but the audio has vanished. What's happening, and what can I do to correct it? Both the iPod and iTunes are running at their most updated versions on a Mac G5 with OS10.4.8. (I have the most recent version of Final Cut Pro installed on my machine, if this could be of any help in converting.)
Can anyone help me out?

you probably didn't choose the right audio format when transfering. Try another format and it should be fine

Thanks Seb481,
Ecxuse my stupidity, but I can't seem to find the utility in iTunes to enable me to do this. The only relevant item from the "Advanced" drop-down for my task is, "convert selection for iPod", seemingly without access to any more fine-tuning options. I've noticed also that the same warning message appears when I try to drag jpegs into my video iPod.
All I'm basically left with at the moment is a bog-standard iPod with a colour screen!(Although, strangely, music videos downloaded fron the iTunes Store play fine. An info check shows them to be MPEG4 files, which is what the above menu option encodes my other video files as, without the audio, however.)
Help!

I'm sorry but i don't think i can be of any further help because i do not use itunes for my conversion and trnsfer. I downloaded my converter at www.ipodmediaselection.com. I actually use this website to download movies as well. There are plenty of sites like this one, you may want to have a look at it.