Saab Dastard:
Note that the picture is a 24-pin DVI-I, there are several flavours of DVI!
There are but for most of the time you need not worry about it....
The pin count on DVI can be seperated to single link and dual link DVI (as I found out).
Single link DVI is the most common standard and allows you to run a resolution of up to 1900x1400 in common monitor parlence. Which is around standard for 22-24" monitors. If you want to go above that you will need Dual link DVI which means the signal is split over an extra set of cables/pins to achieve the resolution - If like me you got hold of a cheap dell 30" monitor you need a dual link dvi cable to achieve the 2560x1600 resolution.
On a quick side note - if you plan to go the dual link dvi route you need to make sure your graphics card can hand dual link - whilst most nvidia cards have dual - dual link dvi (both dvi out can cope with dual link) the recent ATI cards I recall could only cope with dual link on a single primary output.