No problem. If you're lucky enough to be using Windows 98, you can simply copy all the new chipset drivers to the hard drive first, then go into device manager and remove all the hardware from the list, then transfer the drive. When you start the other system with this drive, it will detect hardware and ask for the drivers you've already coppied it. Sometimes after all the drivers are installed you have to do a basic install-over of the operating system to straighten out the system registry, but you won't have to format, so you won't loose your files or programs.
Now if you're using XP it might be a lost cause, you'll probably need to reformat.
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