Computer Science vs Graphics TechnologyWatch
Computer science would most likely lead you towards IT related disciplines being centered around computing and development (software) I dont know what level they'd do at GCSE because when I did mine the most we did was HTML (websites) which was very basic stuff (but it would be at that level)
still its very relevant and could lead well onto a-level or college courses in IT, basicaly this is probably going to point you more towards IT, areas such as networking or software development etc,
Graphics technology sounds to me (I could be wrong) more about graphic design, probalby using image manipulation software to create or modify graphics, again im not sure about the content of this though it sounds more like a graphics design related course.
That wouldnt realy be ideal if you was wanting to go the technical route of IT or perhaps even into programming, but I've known graphics design students in the past go into the web side of development, because non surprisingly graphics and web design go hand in hand, and the code behind it isnt necesarily hard to pick up.
again I dont know enough about the second one, but it sounds like youve got a choice of
IT heavy content (probably some development and networking/hardware stuff)
Graphics heavy content (probably some practical work involing photoshop maybe, more focused on graphics design and its use)
but thats just what I believe,
if you cant do both ask youself what is more important, do you see urself going to uni? if so are you wanting to be a design guy or a tech guy, again thats a real basic way to look at it but thats my take on it
hope any of this helps.