there are three kinds of hidden door "traps", ones with gears one with deer antlers and one with ummm i forget. each one's sucess rate is based on a different stat, I believe magic for the gears one, might for the deer antlers, and something else for the third. basically melee, casters, and ??. the easiest thing is to quicksave, then try to open it, if you fail you take like 80% dmg but nothing else happens (the trap doesn't get destroyed or summon mobs). then reload and try again. once I got one of my characters to like 20 or 25 in each stat I was able to open all the various kinds without ever failing.
you have to always have the detect secrets spell running though while in dungeons, and your character will say something like "somethings around here" to warn you. unfortunately once you open a trap the person keeps saying it, so as you run back and forth over some of the same dungeons it gets confusing as hell.