Check out these videos on YouTube.
You can modify an existing cabinet, but you will be constrained to the size of the cabinet. You probably will not be able to fit anything bigger than a 32" playfield monitor into a standard size pinball cabinet. Others have said that a 28" monitor fits nicely into the backbox as a backglass monitor in a 3 monitor setup.
What are the names of the parts to a pinball table?
Standard Body
Wide Body
Whatever kind you want, but generally you want very flat high quality plywood, 3/4" thick.
It depends on your specific machine. You can contact local glass supply companies who will make them for you. Standard pinball glass is 3/16" thick. You can purchase custom glass from OneDayGlass.com or if you are using standard size glass, you can purchase it through Marco Specialities or Pinball Life (in a two pack).
Almost certainly yes. The monitor, computer and any other hardware will generate a lot of heat without ventilation. You should consider ventilation an important part of your cabinet build.
If you are using a decent computer, and a small size display (32") or LCD instead of plasma or hdtv, then you can get away without any ventilation. Most home users aren't going to have their machine on and actively running intense graphics applications 24/7. The larger the displays, the more the heat will become an issue. A newer model pc handles heat much better, so that the stock cooling in the case should be sufficient.
You of course can do without some or all of these parts, but if you want your machine to be as authentic as possible you will need these:
Ebay or an old machine. If you can find one that has coin mechs and switches, the switches can be used in the simulator. You can also purchase them new from many pinball vendors, such as Marco Specialities, Pinball Life and Bay Area Amusements. Pinball resource, pinball.com and Stern also carry these parts.
If you are tinkering with your cabinet and it has a glass playfield then you need this. Some people make them out of wood because the cost is too high. If cost is a concern I suggest looking for a used cabinet where you get multiple parts at the same time. The cost on a lockdown bar ranges from $100-300 and sometimes you can get a whole used machine for that.
Depending on the size of the monitor you will be using for the playfield, you might want to look at a widebody lockdown bar.
You can find them on ebay, or take one from an old machine. Pinball Resource has new lockdown bars, as well as pinball.com and Stern Pinball even has them available if you call their parts line.
Legs come in several sizes. It really depends on the height you want the cab to be at and how you want it to look. If they are mounted too high or too low it can look awkward.
Some people paint their cabinets black, some people apply custom printed vinyl sideart. There are a few people who have made custom designs and you can ask them if they would share theirs, or you can make your own. You can get them printed through numerous places, including here: Mame Marquees Approximately $150 for both side and backbox artwork. Front panel cost unknown.
aka Where can I see some examples of other people's cabinets?
Here are some great examples of what can be done:
BadBoyBill's nice Ultrapin style cabinet
BryceJ's nice wood rail mini cab / 24" playfield 17" backglass
H4CK3R's DreamPin cabinet, playfield monitor mounted on top of the cabinet -
1up's wood cabinet, not complete
http://www.davesclassicarcade.com/vpinball/vpinball.html
http://pinballchameleon.blogspot.com/2012/12/the-modern-firepower-pinball-project_20.html