Having Frustrating Problem Reading MP4's From New Camera!!! please help:)

I am a professional photographer and have to upload the pictures and videos from the camera from time to time then wipe the memory for new work. Recently, I did a series of pictures and made a video. The pictures show up
but the video is just -not- there. I checked everywhere for it on the folder front but it cannot be found. The upload software that comes with the camera (it's a Sony HX100v) also does not register any video. I know the video is on the memory card because it plays back fine from the cameras own cpu on the little LCD it has. I absolutely must get this video uploaded because it's a very important piece of business. Tonight I even bought a laptop thinking a Windows computer would show it but unfortunately I got XP Pro and after it didn't show up there either found out it might be some Codec or Driver issue? MP4's perhaps are new for the XP Pro and apparently the iMac is having trouble reading it?
The camera is in perfect shape every other way so I would find it hard to believe that it's anything wrong with the reader or the internal memory, cpu, etc.

Is there some problem with iMacs reading MP4 files and if so is there any fix? Would injecting some kind of software/converter/driver or something like this be a solution? Would a separate card reader than what is in the camera for uploads help, i.e. by putting the memory card into a reader would there be better luck, say with some software that comes with the card reader?

Thanks for any help! This is a real tricky and expensive problem. The video is important and I have to get it uploaded as quickly as possible!!!

Well I am actually a fine artist and fine art photographer. I've had no complaints about the quality of my pictures and before upgrading to this camera, was using an outdated Cybershot with a Carl Zeiss lens nowhere near as sophisticated. That got models a lot of work using my pictures and it's mostly in the composition, not the camera. I don't even want an SLR or more expensive one necessarily. This also has an excellent microphone and the video quality I need for my other work.
Secondly, the memory is quite large and I've done a complete session without having to upload already. Sometimes it can be 2-3 sessions before having to upload.
I'm sorry you don't align the logic of my statements to your personal or professional understanding of what I do but certainly do appreciate the help about the formatting issue.
What my solution is going to be (seeing it works or not) is to upgrade my 10.6.7 to 10.8 which I am just about to try from the Mac App store. I need this for another big software upgrade anyway though I do not want to get iMovie '11 unless absolutely necessary because it is not very useful to me outside of uploading the movies from my camera.

Thank you very much!