This FAQ started out concentrating on connecting arcade controls to PCs and a few Mac examples.  Since then however, one of the most requested features has been information on Dreamcast hacking.

Hence, this page.  Not sure how much information this will have as I know nadda about the Dreamcast, but here goes... Edit: I have went through and corrected several things, as I have a Dreamcast and am trying to hack it for using it in my arcade machine. Saint did a great job considering he doesn't even have a Dreamcast. ;) Stuff in red is what I've edited/added  --Tom61

Dreamcast to Arcade Monitor
Dreamcast to Jamma
Dreamcast Arcade Sticks
Dreamcast Gamepad hacking
 

Dreamcast to Arcade Monitor

The Dreamcast natively outputs RGB at 31.5kHz and 15KHz.  Arcade monitors use 15kHz for standard monitors. Medium Res arcade monitors use 25 kHz. The 31KHz from the Dreamcast is for VGA monitors and  will not work with Med. res. monitors. Most arcade monitors, particularly those in older games, are standard res. The scan converter below shouldn't be needed. More info about Dreamcast video modes can be found at  GameSX.com (Note: ignore the mod dealing with SCART, its confusing and unnesscary)
 

There's a gadget called the XRGB-2 Upscan by Micomsoft ($225) available at National Console Support (choose "Dreamcast-accessories" and scroll to the last page) that allows output at the 15khz necessary for standard resolution arcade monitors.  From the web page:

The XRGB-2 upscan converts video from any source into a digital signal for excellent image quality on any VGA or multi-sync monitor. The color of the X-2 is now dark grey as opposed to black sheen on the XRGB-1. The user may now push buttons to toggle between 31khz and 15khz as opposed to tiny, unmanageable dip switches in the original XRGB-1. An on-screen menu allows for easier calibration of modes. Picture quality does not seem to be improved over the first XRGB-1 (how could it be) but this new model offers easier operation and convenience.

MicomSoft's page for the XRGB-2 is here (Japanese only).

Dreamcast to Jamma

Lik-Sang has a Dreamcast-to-Jamma adapter available for $229.  From their web site:

This item is for all those hardcore video game players with a Arcade Machine in their home or even for Arcade Hall owners. The DC Arcade system will let you add the DC machine to your Arcade Rack using the industry standard Arcade connector. The Arcade Joypads, Guns, Steering Wheel or even the coin-counter will work as usual. Dreamcast machine is not included. This new version supports PAL and NTSC systems, as well as NTSC and PAL games.

Dreamcast Arcade Sticks

Not much good on this front - Sega apparently used to sell an arcade stick for the Dreamcast then stopped selling it.  Apparently it's still available from TopShop.com in Australia.

A newgroup discussion on DejaNews debates a variety of available Dreamcast arcade sticks.

Dreamcast Gamepad Hacking

Someone posted a message on a newsgroup about gamepad hacking.  One recommendation:

In my experience, the best is the MadCatz DreamPad.  The actual pad sucks, but you're never going to play on it, so why not? There are non-analog buttons for L and R (labelled C and Z) in the standard 6-button Saturn type setup.  The inside has holes *everywhere* to stick wires through so you don't even have to solder to button connections (anyone that's made a pad KNOWS why this is a great thing), and it's all solid.  I've never had any problems with it....and that's about all I can say. -- (Mike Z)

And the response was:  Finally got around to starting joystick this week and i just wanted to thank you for the suggestion on the madcatz that thing is perfect.  Had a friend over who has much more soldering experience then me do it and he was like thats the easiest thing in the world those holes made it sooooo convinient now all i gotta do is come up with a good design for a case to house the thing in and I'm rockin.  Thanks again for the controller idea.

Note: I don't believe the pad has easy to tap analog stick, meaning games that require it will be unusable, but I could be wrong.

Here's a web page with a writeup on hacking a Dreamcast Arcade stick into a real arcade setup.

 Build Your Own Arcade Style Controls (an excellent site) has a writeup with pictures of how to hack an Interact Astropad for the Dreamcast.  Very well done.

While surfing through the Build Your Own Arcade-Style Controls site (no affiliation, but a good site), I came across some interesting links, including this one:  Ultimate Video Game Accessories sells a product called the Dreamstation that apparently lets you use your PSX controllers in a Dreamcast machine, with the Dreamcast rumble stuff supported.  You can read a review on the Dreamstation here - there are some drawbacks to the Dreamstation so read the review first if you're considering one.

You might consider hacking a PSX pad, and hooking it up via this adapter to your Dreamcast, and... *presto* -- Anyone doing this please let me know how it works! I Have a "Total Control 2" adapter that lets you use PSX game pads on your Dreamcast, works fine in that way, but a standard PSX pad (the kind best for hacking) has no analog controls, and analog controls are hard to hack in general. The TC2 also lets you use a PC keyboard as a Dreamcast keyboard, as well as a controller! This means you can use a programmable keyboard encoder on your Dreamcast for one player's controls! (keymap needed to do this comming soon [they're included in the box it comes in]) I think the best way to do a dedicated multi-player Dreamcast hack with analog support (note: sends 'maximum' whenever you move the joystick, instead of true analog, but gives you full compatability with all DC games), is to hack PowerRamp Mites.  Use one direction pad for the digital pad, and the other for the analog joystick and hook each one to a TC2.