lose of pressure in shower when i use a tap in the house any ideas?

You don't say what type of feed you have to the shower (directly off the mains, both feeds tank fed or even unvented hot water mains pressure).
If you have a tank fed system then you can fit a pump to the shower feeds.
If its mains pressure direct then another tap being used will reduce the pressure. As far as I'm aware the Water Bylaws prohibit pumps being fitted. Someone correct this if I'm wrong.

Stephen
November 2007