USB Game Pads Hack
The current version of MAME supports USB game pads. thus you can hack a USB game pad for your controls. Simplely take apart the game pad, solder wire to the contact points on the game pad to your arcade button switches. You will need to enable USB in one of the MAME .ini file. (sry idk which one, some one edit this part: ) ) Next you will need to set the player controls from the keyboard to the USB bottuns.