I'm not so certain that an external hard drive is a viable option. However, if you have an extra one that is easily removed from the case, put a 2nd hard drive in the computer - unless it's a laptop...
Moving the Library folder isn't so bad, and can be set-up prior to going to sleep at night, and will most likely be done just a couple hours later. If all you have installed is SH4, then it might not be more than an hour. If you're like my kids, where the page scrolls 3 times, it might take the better part of a day...
