Ok it's not the AGP/PCI-E problem. Problems I'm having right now is the huge processor heatsink and the undersized casing. For detailed information, please refer to http://forum.lowyat.net/topic/1122747 .
So what can I do now ? Is it possible to just purchase a smaller heatsink and change the casing to a bigger one ?
1. Are you sure that your psu can sustain the whole rig?
2. Is your cpu P4 3,4ghz? If it is, I thik it will bottlenick the gpu.
3. You can take out the plastic case from the cpu. Maybe you will have more space.
Anyway you will have a big problem with temps. All the hot air from cpu will go to the gpu.