To turn off your xp, visit the XP guy in Stormwind Keep, in the pvp room. A level 19 rogue should be stealthed but visible. He requires a few of 10g. Idk where the horde equivalent to that is but I assume it would be in the same room. That's the only way you can do "twink" bgs without gaining xp, or if you only have TBC Expansion.