Again, it's not a ventilation issue. If you actually take a 360 completely apart you'll know why I say that. The reason most of them had the error relating to the graphics chip was as follows:
1. The crappy "thermal-tape" used wasn't effective enough at transferring heat from the chips (cpu and gpu) to the heatsinks.
2. The crappy X-clamp design of holding the heatsinks onto the 360 mainboard didn't take into account what might happen if the board were to flex.....say from excessive heat.
So we had this happening:
1. The crappy thermal-tape couldn't do it's job well enough so the chips/board got too hot
2. This caused the board to flex
3. This caused the stupid X-clamp to no longer have the heatsinks forced down onto the chips with enough force!
4. This caused the GPU to overheat in seconds, freeze and throw the error code about a GPU error!
Some people on the internet even suggested wrapping the xbox in a towel and forcing it to overheat (the entire xbox instead of just the graphics chip and the area on the board around the chip). This worked usually for about a week or two because what those people essentially did was to warp the ENTIRE 360 mainboard in the hopes that the heatsink and clamp would straighten out a bit.
The only way to correctly fix the problem/issue is to do exactly what I described in my earlier post. Something I haven't only performed on my own xbox's but also on those of friends and family with a 100% success-rate. edit: oh and no two-week waiting period! hehe 
the Monk