Due to the fact that all you have is basically a recovery CD from your other system you will need to purchase a new copy of Windows if that is the OS you wish to use. The recovery CD is going to be looking for hardware that is in your old system and when it doesn't find it, it will fail to run. If you are going to be doing an upgrade though, there is a possibility that you will not have to redo your installation of the OS.
From the sound of things you are not going to be replacing the hard drive in the system. In order for you to get the system up and running with the current OS on the existing hard drive there are steps you can take to update the drivers on the existing Windows install.
First off, when you have installed the hardware you are replacing, the motherboard is likely to require drivers that are not currently installed on the hard drive. Your best bet will be to boot the system into safe mode right from the start so that you can install drivers, or at the very least uninstall drivers for hardware that no longer exists. To do this you would press the F8 key until the boot options screen appears. Start pressing it right when you see the first indication that the system is attempting to load Windows and repeat pressing it until you see the screen with the boot options. Once on that screen, choose to boot to safe mode. Once in safe mode you can attempt to install the new drivers from the installation CD/DVD that came with the motherboard. This is likely to fail, but is worth a try.
If this fails you will need to identify drivers in the device manager and delete the drivers that are from the old motherboard. There can be several areas that will affect the system's ability to be able to boot into Windows normally. If you are unsure at this point what needs to be replace it might be a good idea to have someone who is familiar with installing hardware present so they can direct you on which drivers/hardware needs the update. If you are familiar just deleting the devices and rebooting should be enough to allow you to boot to Windows with minimum drivers so that the system asks for the manufacturer's disk to install the drivers.
Be careful when attempting this as you may make it to where the system won't even boot into safe mode if you remove the wrong items. If that happens, you will be back to needing a new version of the OS in order to install Windows. I would highly recommend that you create a backup of all your important information prior to doing any of these steps in case you have to wipe the drive and start over.
