Typically the laptop cases are designed to operate within a certain temperature range, and if yours is over heating, it could be that the heatsink or fan on the CPU is not working properly; so cutting holes or extra vent slots won't necessarily solve the problem.
I have one of these - the cooling system is a large heatsink/fan assembly cooling the cpu and what appears to be a chipset chip. The fan is a centrifugal type, positioned over an access hole in the motherboard which in turn is situated over an area of the case that seems to have an unrealised vent through the underside case plastic. Given the position and design of the fan, it seems to have been intended to draw air up through the bottom of the case to be vented through a vent on the back. The back vent is open, the bottom vent is present in outline, but not open. This appears to be a design flaw, a thought which is borne out by my own experiences with this laptop.
I have a couple of brothers who helped me with my own (severe) overheating issue. I dismantled the laptop, replaced the heatsink compound where it was needed. They drilled the bottom vent such that it now forms a grille according to the original factory impression. My laptop was running at 75C and 550MHz for both cores prior to the modification. Now, it runs at 2200MHz and 56C, both cores, under heavy video processing load. The newly opened vent pulls cool air from the underside of the case - hot air is vented through the back vent. This appears, as stated, to have been the original design intention.
Prior to the mod, the fan was essentially just recirculating the warm air already present in the case, an observation backed up by the absence of large amounts of dust.
My brothers opened up the existing vent slats, but an easier modification for someone who *isn't* a wizard at dremel use, would be to cut the square grille area open on the underside of the case, and using a good quality glue like slow-curing epoxy, glue a fine plastic mesh in over the square (on the inside of the case botton) to cover the grille.
Do this only if you have bad heat problems, and only if you're confident of completing the modification without ruining the case.