The software keyboard has some buttons on the upper left portion that control the input whether it's Kanji or Western. Screw around with those until you get the right combination. I believe the same thing is accomplished via the two function keys to the left of the -@ key [beside the space bar] on the hardware keyboard.
I owned a c760 prior to getting the c860, and am NOT a big fan of the new Sharp ROM. You might think about installing the CACKO/Sharp-based rom before you get too far.
The desktop sync software should install the same as the manual describes.