Best method would be to run the first boot after swapping from the win 7 install disk and run a REPAIR INSTALL -- this forces the OS to reevaluate the system and install drivers for the hardware that it finds installed on the system -- by doing this it will get rid of any old drivers fro non existent hardware and install the needed drivers for the new hardware without messing with the software programs and files that are on the HDD and will in most cases save you from having to do a complete reinstall.
After it runs and you reboot go into the Device manager and ensure that there are no yellow warning signs on components that may not have installed properly and correct any issues noted and you should be good to go (though swapping the CPU and MOBO will also most likely deactivate the install so you will need to reactivate it by running the activation wizard and most likely going through the phone activation process and\or talking to a rep in order to get it activated since those are considered major components and MS will want to ensure that it is in fact the same system and that the OS is only being used on the one system. (NOTE : technically it could be considered a new system and require the purchase of a new OS license if it is an OEM install, as the license is tied to the original mobo that it is installed on but MS is usually pretty good about allowing reactivations as long as it has not been used several times already.