Great photos and breakdown of the Willcom (Sharp) D4 at PC Watch. It is in Japanese so grab your favorite website translator (Google’s works great) and get a look at the D4 all naked. Some nice findings are that it uses Toshiba's 1.8-inch HDD, "MK4009GAL HDD so finding a larger HDD should not be a problem. Of course, cracking the computer apart like this will shred any warranty it had. See more pictures and read more with Googles’s translation.
Go to the Japanese site here