Windows Vista Home premium - Problems installing new software

I've been using an XPS 420 for almost a year without any serious problems. Over the last week/10 days i have tried to install 3 pieces of new, Vista compatible software, all from know reputable sources (Nikon, Microsoft...)

The PC loads the DVD and installation starts. Install wizard opens,  country option is chosen and almost immediately the installation terminates due to an unknown / unspecified error.

I have tried to restore the system using the Vista option but again another error is shown

%1 is not a valid windows application.  (0x800700C1)

I also have a Toshiba laptop running Vista home premium and the software installs and runs fine on thsi much lower spec machine.

I have tried everything I can to correc the problem but have now run out of ideas, any help would be appreciated

Thanks