lol, this board is getting pretty good at hazing the new guys and giving them grief (I'm included in this, so I'm allowed to say it

)
Tzatziki, your questions are most certainly NOT specific to your cabinet. Regardless of cabinet, the process of converting to mame is the same (in a general sense).
Ultimarc.com will give you a lot of info on your Ipac, including how to wire it. Your cab isn't JAMMA, so I'm not familiar with your wiring.
My best advice is to read, read read. All of your questions have been answered. Read the forum, arcadecontrols.com, and all the example pages you can. I guarantee you'll answer your questions and figure out things you were wondering about.
So as not to just tell you to read though, I'll try to answer your questions really quickly.
1) You'll know which wire to hook up because it will be corresponding. player 1, button 1 goes to P1,B1 on Ipac.. simple. Soldering iron isn't required. Use quick disconnects and the screw terminals on the ipac.
2)each button has a wire to the ipac.
3)depends on what games you want to run. READ READ READ, this comes up everyday. You don't "need" an arcade VGA, but its the easiest way
4) Not needed, may be handy though.
5) um... MAME is the emulator.... so ..... Mame is the best mame to use

6) this is like the same question as 1 and 2. Read up man.
7) One power supply is plenty, but it will depend on what you have in your cab.

A few different optons. Read the software forum
9) The Ipac doesn't, but MAME can.
10) hack amplified PC speakers or just use PC speakers.
11) You don't really "need" to keep anything. Keep the monitor if it works and thats what you want, and the isolation transformer (if applicable). Game board, PSU, wiring, etc can be taken out if you'd like.
Now get to reading, there will be a quiz tomorrow
