What type motherboard n processor will fit my machine?

i don't know reasonable price mean to you but HP Pavilion A1700N come with Vista Home Premium mean you must looking for Motherboard that ready for Direct X 10 that support vista (Onboard VGA 8 series) or if you buy separate VGA card you can try Asus P5BMX (the price below $100), and so you need dual core processor or higher depend on your budget