drill a hole

Thanks mate, shouldn't need a crossover as my head unit has a built in highpass filter for front and rear channels, so I can set the front channels for 200 hz highpass and connect the rear channels to the crossover you get with the components to filter the unwanted high frequencies. Any ideas how to get new wires into the front doors easily?

Yes, I would use the fronts to run tweeters and rears to run the midrage woofers.
Crossovers will be needed to use this set up. (I wouldn't solder anything though)
go for focal comps.

I have a 4 speaker Sony CDXM770 Active black headunit which up to now I have used to drive 17cm front components and rear shelf mounted 6x9s. I have recently started using the car for 1/4 mile racing and have had to strip out as much weight as possible so the rear shelf and speakers have to go. I will be keeping my head unit and front speakers as I need some sounds;) Would I be best to solder the front and rear channels together to give all the head unit power to the front speakers as I see little point in leaving the head unit's rear amplifiers doing nothing. Another option would be to use the front channels to drive the tweeter and the rears for the bass speaker, though I would have to run more wire into the doors for that which insn't easy on the corsa. As I am down to fronts only I will probably upgrade my front components as well. What 17cm speakers do you suggest that sound the best and produce good bass, but still will fit in the front doors using the audioleads adapter. My budget will be in the region of 150 pounds.

cheers

Alan