yeah, the only emulator worth playing on your Dreamcast is NesterDC since it runs full speed with the newest version. If your X-Arcade isn't working on NesterDC, try updating it by going on Google and searchin for "Daily NesterDC" and there's this japanese guy who fixes bugs daily and updates versions of NesterDC. Also, just to make sure it's the X-Arcade, try turning on NesterDC with the X-Arcade plugged in, try moving around or whatever, then put your own dreamcast pads in there, and try moving it then, then going back to the X-Arcade, just to make sure it's all the X-Arcades fault. The only problem I had with NesterDC once (I use PSX to DC for my arcade stick) is that in Contra, I had the 2nd player controlling both guys, but i just put in a differnet version of NesterDC and it ran fine, it was kinda weird, probably a one time kinda bug. BTW: if you do get the dreamcast NES emulator, you gotta get Crash And The Boys Street Challenge, and Super Dodgeball, believe me, 4 player NES games are way more fun than you remember, especially while not sober... I mean....
-good luck
-CthulhuLuke