[Darthtanion]

1- Get a vacuum cleaner with a hose attachment and a can of compressed air and clean the dust out of the entire machine. Pay special attention to all heatsinks since it is highly likely you have an excess buildup of dust and gunk in the fins. This will greatly reduce the cooling ability of the heatsink. You should do this regularly if you are going to continue using that window fan unit since it has no filter system in place and all teh dust in your home will end up in your box.

2- I can't tell for sure from the angle of your photo, but is there a fan on the heatpipe cooler of your video card? Since this is where you feel the problem lies, this is a good place to start. Aftermarket coolers are not generally very expensive so a better cooler may be in order.

3- Try to reduce your cable clutter. All those cables hanging out into the open airways isn't giving your enclosure a solid path for the air to flow through. Airflow is important since it keeps cooler air circulating over the hot components. Even the world best heatsink can't do much good if it only has hot air passing over it. The cooler air helps dissipate heat.

4- That case doesn't have a lot going for it. Not only does it look to be an OEM type enclosure, the smaller size doesn't give you a lot of room to modify. Maybe a intake fan on the side panel (over the video card/CPU area is best) and an exhaust on the roof would be about the extent of your play room.