Open up your .mov file in QuickTime Pro 7. Click "File" at the top, then click "Export". (Screeshot below)
Click the down arrow of the "Export:" box rightside and select "Movie to MPRG-4". Then click the "Options" button. (Screeshot below)
Then select "MP4" in the "MPEG-4 Export Settings" dialog-box to choose the codec that you want to use for the compression. Under the "Video" section, there are just 5 options for "Video Format" (Codec) choosing: "None", "MPEG-4 Basic", "MPEG-4 Improved", "H.264" and "Pass Through". (Screeshot below)
For Standard-Definition MP4 movies in normal size, keep "MPEG-4 Basic" the QuickTime chose, and set the "Data Rate" a litte more than the default setting "64 kbits/sec" with a higher "Image Size" Hint: Never set the "Data Rate" over the mark of 9000 kbits/sec if you select "Iamge Size" in "768 x 576 SD".
But if you want a High-Definition movie, please choose the "Video Format" as "MPEG-4 Improved" or "H.264", and select the "Image Size" in "1280 x 720 HD" or "1920 x 1080 HD" after "Data Rate" changes. DO REMEMBER: Never set the "Data Rate" less than "6000 kbits/sec" if you want to get a real High-Definition quality movie!
Now it's time to decorate the "Audio" settings as we did the in "Video" settings. Before that, you are supposed to check the actual rate of the orginial audio and select the rate that matches the orginial to aviod having sound sync crashed.
Backward to the "MPEG-4 Export Settings" dialog-box to choose "Audio". Set it to 48 kHz stereo (16 bit default) for the best audio settings, and click the "OK" button. (Screenshot below). 
Right now, just keep going with OK-click until back to the "Save exported file as" window, locate the destination folder on your hard drive with enough free space and click "Save". Well done! Just wait for it to finish. (Screenshot below) 
Once the processing finished, you have just managed to successfully convert your .mov file to Standard-Definition MP4 and High-Definition MP4 format with QuickTime Pro 7. There are more tools which can help convert MOV to MP4 files compatible with multiple portable devices, and you can find more guides about How to convert MOV to MP4.