The information below comes from Marvin, so if you have questions, send him email.

              DREAMCAST A/V CONNECTOR
   ______________________________________
  |                                      |
  |1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16|
   \____________________________________/ 

  1   Ground              to VGA pin 6 / Scart pin  4
  2   Audio OUT right                 to Scart pin  1 (2)
  3   Audio OUT left                  to Scart pin  3 (6)
  4   +12V                over 4k7    to Scart pin  8
  5   +5V                 over 220R   to Scart pin 16
  6   video out config    31kHz  (VGA)   (connect to ground)
  7   video out config    RGB out (TV)   (connect to ground)
  8   VSync for VGA       to VGA pin 14
  9   HSync for VGA       to VGA pin 13
  10  CSync                           to Scart pin 19 (20)
  11  S/VHS
  12  S/VHS
  13  Composite Video     'normal' Video OUT
  14  Blue OUT for VGA    to VGA pin 3 / Scart pin  7
  15  Green OUT for VGA   to VGA pin 2 / Scart pin 11
  16  Red OUT for VGA     to VGA pin 1 / Scart pin 15

!!       I used a female Scart connector             !!
!! (pin numbers in brackets are for male connector)  !!

For HSync and VSync a little bit of electronics is needed:

                          +5V
                           |
                          | | 4,7 K Resistor
                          | |
    pin 2(4)  18(16)       |
DC ---------|>-------------+--------- VGA
         Driver           _|_
                          / \ 1N1418
          74244           ~|~ (or similar Diode)
                           |
                          GND

pin 20 is +5V   pins 1,10,19 go to Ground

pins 2 and 18 are for HSync / 4 and 16 for VSync

RGB signals should be buffered by a 100yF capacitor
               +
DC -------------||------------------ VGA/Scart

Soldering points on DC PCB:

     <--- Back of DC
     |    o n.c.
   A | o    16
   / |    o 15  Thats all for now... (ok the original VGABOX contains
   V | o    14  two opamps for audio but these are not needed)
     |    o 13 
   O | o    12 Isn't it a shame that the VGABOX is so expensive :)
   U |    o 11
   T | o    10
     |    o  9             by ...:::Marvin:::...
     | o     8
     |    o  7
     | o     6             Marvin@sol.de
     |    o  5
     | o     4
     | 
    1| o   o 2
     |
n.c. | o o   3