You would need to buy a valid retail license for Windows 7.  The license that comes with the computer is called OEM, is specific to Dell, and is restricted to the computer with which it shipped.  Generally, the installation disk will check the BIOS to see if it is a Dell system; if not, it will usually abort the install.  I've heard of instances where it will install, but in any case, it will not accept the Product Key for activation. Other things to watch out for, which are common for this type of project ... various control panel and peripheral devices in the system do not always have standard connectors, so sometimes rewireing a connector is necessary.  I can't say for certain for the 8300 in particular.  Also the alignment of mounting holes can affect how easily other boards can be used.
Hi Everyone, I have an XPS 8300 i7.  I want to change the existing motherboard to Asus P8P67 PRO.  Has anyone done anything similar and faced any problems?  Mainly, any problems with a re-install of Win 7 from recovery discs.  Does anyone know the Dell motherboard is linked to the Win 7 install?  Thanks in advance
XPS 8300 Motherboard Upgrade - What OS Problems Will I Have?