Here is a list of the software that's inside my cabinet:

Win98 DOS
As the pc is in a PC2JAMMA-cabinet, DOS is the way to go, making it possible to use the original monitor. Using the Win98-version enables me to have partition-sizes > 2Gb, with Fat32 for 4Kb clusters. This is very usefull for all the small games.
MS Network Client 3.0
The network client (available at Microsoft's ftp-site) enables me to update the software on the arcade-pc, without opening the cabinet and taking out the pc. Remember that my arcade-pc doesn't have a floppy or CD-Rom drive, so network-access is *really* needed.
Arcade OS (always the most current version)
The main 'interface'. Arcade OS enables me to use the various emulators inside the cabinet. It also gives me a arcade-monitor compatible dos-prompt.
MAME (always the latest non-beta version)
Of course, MAME. Using the latest non-beta version gives me sort of a steady environment. It also means I don't have to be hunting roms each other week, I just update the roms on my other pc whenever I have some spare time. If another release candidate is appearing, I'll get my set's completed, will do a full merge, et voila.
Dragon's Lair
ReadySoft made a port for the PC. I'll just need to get it working for a non-cdrom system, but this isn't on my high-priority list.
Space Ace
Also the ReadySoft version.