You might try consulting the EPE LCD guide?, it's an excellent introduction to LCD's.
If you check my initialisation above, you have to send 0x20 first, this switches the LCD to 4 bit mode, then you can send 0x28 which sets the rest of that byte up - you can't just send that in the first place, as the lower nibble would be ignored until it's in 4 bit mode.
I have a printed copy of the datasheet of the Hitachi 44780 controller. The images on the second link you've posted are copied from there.
You can find the instructions set in the datasheet.