you can get partially assembled barebones kits and then configure them a little yourself, but it's prohibitively expensive, not much variety of compatible parts, and like you said a pain in the arse to build too... :/
I have a laptop that has switchable integrated Radeon 3200 and discreet 4330 graphics, on a 1366x768 display. Using the 3200 (weaker than a 4200) I get 45 fps on Guild Wars with max settings, while running around in ABs. It dips down to ~15-20 fps with heavy action but it's perfectly playable on max settings. Kind of surprising.
You're playing at a relatively low resolution so it's not that surprising you get that kind of performance, GW is 5 years old after all. As a comparison, the 9650M GT in my old laptop drops under 60fps at 1440x900 in certain areas of nf and eotn when it gets busy.
If the OP want to play at these resolutions, he will need a bit more horsepower for max settings. Oblivion was also mentioned and if you have the extra horsepower to use high texture mods, it's definitely worth it.