I am trying to install Windows Server 2008 R2 onto a different hard drive that I'm going to put in the other computer and I keep getting that error. I would like to know the reason of this as soon as possible. Thanks.
Thats not allowed... the motherboard drivers are loaded at install time and this other computer has a different motherboard (therefore needs different drivers). You can sometimes get around it by using the exact same motherboard on both machines or a default vmware set of drivers. note that without that error your board would now be dead because you put the wrong power into it.
Actually this is not entirely correct, you can make modifications to the registry to enable base IDE/AHCI drivers so that the install is more generic and will move to a different system successfully in most cases.
Windows Setup disables these boot modes as setup runs to speed up boot times, as it only needs to load the drivers that correspond with the system you are currently on.
Commonly the values can be find at
These services's Start value can be set to 0 to re-enable them. You can set both of the Start values to 0, power down the OS and insert the drive into the new machine and you might have success. The other hurdle you might run into is that you may need to install the correct driver for the target server (or computer)'s IDE/SATA/RAID interface before you power down so that it will be available to the new motherboard when it boots. Another option would be to use sysprep, but I wont go into that as its a topic of its own.