many thanks for sharing your experiance of macs. In view of this i have decided not to go for the model with the intergrated nvidia geforce 9400 graphics but to go for the imac 24inch with 2.93ghz , 4 gig of memory and the the  dedicated  nvidia geforce gt120 with 256 mb of memory.

This will bump up the price by £300 and mean i have to save up my money for a few more weeks but in the long term should be a better investment and give more satisfaction.