Wow! Lots of questions to answer. I'll do my best...
Currently I have it working with MAME, Gens (Sega Genesis), Visual Boy Advance (Gameboy Advance), and Daphne (Laserdisc games). Will probably get to Super Nintendo sometime this week.
If you are running this on an arcade monitor at 640x480 (interlaced), you will need to adjust the default font sizes used to draw the text. To do this, launch myHTPC Config and select "Default Theme" in the tree. From there you can change the font and font size for each type of menu element (titles, captions, menus, etc.). I'm not near the machine right now so I can't post my values, but I'll post them tomorrow.
To make the interface work without having to use a keyboard and mouse, click the Remote Control item in the configuration tree. You can then assign commands for up, down, left, right, select and back. My cabinet is connected via a JPAC so the controls are mapped to keys. In order to assign a key in myHTPC, just press the "key" button. Note that you might not be able to see the "key" button at 640x480. You may need to temporarily raise your resolution for this part of the setup.
On my system the joystick moves the highlight up/down/left/right, button one is "select" and button 2 is "back". I also set the Mouse Pointer option to "hide all the time". You don't need a keyboard and mouse after you have it set up properly.
To download cover art for CD's, I just use Windows Media Player 9. Drop in a CD and it should automatically download and cache the CD cover.
To download cover art for DVD's, I currently use Collectorz.com Movie Collector. You could also just download the covers from the very nice archive at
www.dvdempire.com.
As for connecting it to a DVD/CD megaplayer (I assume you mean an externally controlled device) that is beyond me. However I'm sure there are plenty of people at
www.myhtpc.org and
www.girder.nl who can help you get this working quite nicely.
MyHTPC doesn't run off scripts. It has a Win32 configuration program where you add media modules. What you need to do is add a media module for each "Player" you intend to use. For example, in my case I have media modules for MAME, Gens, Daphne, and VBA. You then need to create a database file (called a .my file) that contains information about your collection. There is a fantastic tool called myGames (linked in my first post) that will automatically scan your ROMs and create a .my file for you.
So to set myHTPC up for MAME, you would do something like this:
1. Open the configuration program
2. Add a media module, name it "MAME"
3. Under "grouping method" select "single metadata file"
4. Browse to the .my file you created using .myGames
5. Turn off all the "cache" checkboxes and press "build now".
NOTE: If you have < 500 Roms this will just take a few seconds to build. If you have more then be prepared to wait for several hours as myHTPC tries to sort the data. This is a known bug and will be fixed in a future version of myHTPC. If you have a full set just click "build now" before you go to bed at night and it will be done in the morning.
6. Under "Player" select the "myHTPC_ExeMp.dll" Plugin DLL
7. Enter the path to the MAME executable under "executable"
8. Enter the path to the MAME folder under "current directory"
That should get you up and running! The rest of the settings you can tweak with on your own.
To get this working with other emulators may required the use of Girder. For example, pressing "ESC" quits MAME, but not VBA or Gens. So you will need to create Girder events to quit those apps upon receiving the ESC combination from your arcade controls.
While it is definitely a bit of work to get this up and running, the results are well worth it. I now have a complete, seamless interface for all my emulation programs with a consistent user interface that does not require a keyboard or mouse to navigate.
Hope this answers the major questions. More help can be found over at the myHTPC message boards.
Patrick