Keyboard Clashes, Ghost Keys and CALLUS
If you're just using MAME you should be pretty much okay, (although left/up/alt together didn't work on my keyboard) but there is a problem if you want to use the standard MAME keys with CALLUS.
If you're running CALLUS and you press the standard MAME button 3 (space) CALLUS' GUI appears, if 2 people are playing on CALLUS and player1 presses button2, and player2 presses button3 - CALLUS quits ('cause you just pressed Alt-Q)
My advice is to remap button2 and button3 to something other than Alt and Space (I use N and Z). It's a pain to go through every single MAME game and remap the keys, so I wrote a small utility (MAMESET.EXE) which allows you to remap the keys in all games.
Notes on 8Way / 4Way Joysticks"
A lot of older Games (PacMan,Ghosts n Goblins, Amidar etc.) had 4 way joysticks in their cabinets. Which meant that it was impossible to do diagonal movements in those games.
If you play these games using a modern 8Way joystick - you may come across problems (such as being stuck on a ladder in GnG or going the wrong way in PacMan).
If you play the games 'cleanly' (i.e. don't don't use diagonals) it won't be a problem but a better solution is to use an 8Way/4Way joystick in your cabinet These are normal 8Way joysticks with a 'plate' or 'mask' on the back. This mask is a square with rounded corners and can be rotated 90 degrees. At one setting - it's a normal 8Way Joystick, at the other it's a 4Way.
I have one of these joysticks in my PC2JAMMA cabinet and it DOES make a difference
Well that's basically it - you should now have enough information to make your own PC2JAMMA adaptor
Here's a few shots of games running on a PC in a Cabinet