im installing a computer in my '94 GTI with the same stock dash setup as your '94 jetta. im planning on revamping almost the entire dash to make room for the lcd and other features i want in it but there are a few options you have without completely rebuilding... you can mount the LCD in the storage/cup holder area like this... [media]http://members.aol.com/ProGolfr15/LCDJetta.jpg[/media]
if you didnt mind relocating the radio you could mount like this... [media]http://anti-freez.net/pics/carputer/sh0cker_02.jpg[/media]
^it's kind of a big LCD... im guessing 10.4 inch or something like that
orrrrr you can do what i plan on doing... im planning on installing a 7" lilliput 629 in the center trim area. im going to relocate (or possibly convert to electronic controls) the fan speed, air temp, and air direction dials and also relocate all the buttons (rear defroster, p.locks, a/c, etc) similar to this 3d model...
it's not a complete model but it gives you an idea of the LCD fit. the outside dimensions are pretty close to the workable area you have in the dash and the LCD screen and bezel are dimensioned to the manufacturers specs of a lilliput 629. where the dash starts to angle backwards is the area that the ash tray and cigarette lighter is (the circles are areas allocated for toggle switches to control various functions). the cupholders in my opinion are useless so i may modify my design slightly to incorporate that space but ultimately i need my LCD to be as high as possible for viewability.
i was toying with the idea of putting the LCD up in the above trim area to replace the headunit spot and the air vents but im not sure about that just yet.
hope that helps.