I mainly enjoy the classic games as well as many first generation NES games. I think a 2 player setup with 6 buttons would play most of what I need. What is the preferred layout for the buttons? What functions would each of the buttons have?
If you don't plan on playing non NeoGeo fighting games you can get away with just 4 buttons per player, but most peole tend to go with the 6 button layout, as Tiger-Heli mentioned. There are some threads over in the Software Forum about setting up .CFG and .INI files to automatically take care of the re-assignment problem Tiger-Heli mentioned.
What kind of software program can I use to interface with the emulators I want to use? Is there something that will automatically start when I start Windows XP?
Most of the Front-ends out there will do this, and certainly the "big three" of Mamewah, Dragon King, and Kymaera have that ability. Just make sure you read through the threads here and the documentation that comes with the software. You'll run into a lot fewer headaches that way, and you'll learn from the rest of our mistakes.
As mentioned, you can get any program to run on start-up by simply putting it in your startup folder on the start menu. There are other ways of making it happen as well, but that's the simplest.
This is almost overwhelming with all the information available.
No "almost" about it, it *is* overwhelming, and there's always more to be learned and dug into. Just break up your project into smaller tasks, and focus on those tasks only un til they are complete. My recommendations:
1. Get the emulators installed, and learn how to use them without a front-end. This way you'll learn what is a potential front-end error, and what is an emulator error. You'll also get to play games faster. There are several different emulators for the consoles, so experiment a bit to find what works best for you.
2. Install and configure a front-end to work with one emulator (usually MAME, as most of the front ends have default settingsto work with MAME). Now you can start to think about the look and feel of your front-end, and what skins you'll want to use.
3. Configure the other emulators to work in your front-end.
The nice thing about these three steps is that you aren't spending money, and can be saving in the background for the expensive items later.
4. Now you start buying, buy your encoder, buttons, and Joysticks (and wire and quick disconnects). In addition to the online retailers, there are several ebay stores that sell pre-packaged packs of buttons and joysticks. I paid ~$36 for two Happ Ultimates, P1-P2 start buttons and 12 players buttons. Not the cheapest, but very convenient. Learn how to wire the switches and configure the Encoder.
5. Experiment with your layouts. A double thick piece of foam core is really cheap and can help you get a feel for how you want to do your final layout of your control panel. Better to spend $2 and prototype rather than waste a $5 piece of wood later.
6. At this point you may want to start building, so build your Control panel, and maybe a temporary enclosure for it.
7. Now you get into the big buidling of the cabinet, getting a monitor, etc.
8. Now that everything's together, tackle the artwork and really make it look nice.
Of course, you may want to do it a different way, and there's no wrong order, but by breaking it up into smaller tasks, you aren't overwhelming yourself. By doing the big building last, if you stall, you aren't stuck with a half-finished cabinet in your house for a year (Like I have).
Above all, keep reading and learning on these forums. I think you'll find that the people here are about the nicest group of individuals on the Internet.