upgradinging the graphic card like you suggest. The 7300 is the low end Nvidia GPU (graphics processing unit) whereas the 7600 is more mid-range. Also the 7600 supports HDTV, so it's a bit more futureproof.
The MESH monitor seems fine to me, since you won't be playing high end games at top setting the 8ms response time is fine, its what most monitors have. Also, you'll be hard pushed to find a decent 19" monitor for £110 (which is how much is subtracted if you take it off) and if anything goes wrong it's covered by MESH's warranty. However, it's DVI sodon't forget to add the DVI cable for £5 underneath unless you already have one, otherwise you'll get a PC with no way to connect it to the monitor! DVI is not to be confused with VGA, the blue port you see on older monitors and graphics cards, as far as I'm aware the two aren't compatible. I'm still on VGA because my system is 5 years old, but I'm pretty sure ports are different.