does any one have any clue how to increase the pressure of the 405 sti brake for better and much responsive braking?? and another question is does the 406 springs fit on the 405 suspension?? and will it be lower springs or the same height as the 405 sti standard springs?? and will it give better handling?? thanks in advance

Might help to either fit a larger brake servo fraom a 406 maybe.. or adjust the servo rod a little bit so it will engange more brutal to have more "response".

Other than that it might help with better pads also, but the responsiveness should be mostly from mastercylinder/servo setup.

However I noticed big difference in response after fitting braided brake hoses to my 205, so that might be a place to start, not as spongy feel anymore.

thanks, do u have a pic of the servo rod?? and how do i adjust it? and what about the 406 springs?? do they fit in the 405?? and are they shorter and better handles??

There are a few ways to go about this.

1. Change the master cylinder to the one from Peugeot 406 (it's either 23.4 or 23.7mm, can't remember)
2. Change the master cylinder to a performance one (like I am doing - a race tandem master with 2x25,4mm masters with separate lines and brake fluid reservoirs) and Wilwood brake bias valves.
3. Change the servo to a larger one (255mm for a 405 with ABS brakes, a bit larger for 405 T16 one, and yet larger for 406, etc.)
4. Fitting braided brake lines
5. Fitting performance disks and pads (this will also have a dramatic effect when braking on track or from high speeds)
6. Fitting larger calipers (e.g. 4-pot Brembos, Wilwoods etc.) - this will trigger all of the above upgrades as well.

Oh and some say that ridding the ABS helps avoid that spongy pedal feel as well.

the 406 springs are unlikely to be a good fit. even if they do fit, they are not performance oriented, and the car will likely to sit higher that on 405 springs as 406 weighs more.
the best option apart from coilovers IMHO is fitting performance springs for a 306.