This motherboard in a nutshell will not support a core 2 duo chip... this motherboard is based on the intel 915 chipset which was for early 775 based pentium 4's
This is your motherboard..http://h10025.www1.hp.com/ewfrf/wc/document?lc=en&dlc=en&cc=uk&lang=en&product=458301&docname=c00196251
you will need to replace this with a newer Intel Chipset based motherboard and replace the processor..
the video card will be ok but I would recommend getting some ddr2-800.
failing that replace the whole machine as this is about 5 - 6 years old and you should start again from new.
hope this helps