Software update error

Hi

I have been having a slight problem with software updates in the last month, I bought my mac about august last year, and i updated my software the other week it downloaded it all fine but when i restarted the computer and the updates began installing half way through a box came up telling me there had been an error and no updates had been installed, I'm not a computer genius so I have no idea what to do, could anyone help me sort this problem, all help is greatly appreciated thanks a lot
Max

 

thanks for your help, but it seems not to be with just updates i just tried to install a copy of logic express i just got and i did it 3 or 4 times aand it kept saying instllation error then i triad to instal the 10.6.7 combo update you advised for me and that didnt work either, its really anoyinh i can't install anything