Secret to opening Sharp PC-G850VS?

[Zaphod]

Remove the six screws .... remove both port covers then gently:

Stick your thumb/fingernail into any of the corners (in the hard cover slide slot) as a wedge , and tease the corner apart gently.

I seem to recall I started at the end away from the battery compartment (because as you near the end of the process you have to help the two 'soldered onto the board' battery springs through the rear casing (they stay on the pcb obviously))

You will find there are locking lugs along all edges (think there were 3 along each long edge, and a similar mechanism on the short sides)
It's a fairly standard way of locking a casing together.

Once you pull one open you can determine whether it's the top or the bottom that has the tab, this will allow you to manipulate the case to release each tab in turn.
(It's a case of gently pushing the top or the bottom slightly inwards (to help release that tab) as you tease the case apart at that point, then move on to the next one.)
Release both long sides and one short, then move to the last short edge. (This should be the battery door end)

Be gentle and you won't break anything.

Did I mention gently?

If you have any trouble I'll open mine again and try and get more tips for you.