Question on concerning DC's for D&D

[Xyvol]

Do you guys play Dungeons and Dragons? I'm working on making an adventure for my group to play at some point. I wanted to know if there are any guidelines for Difficulty Checks. If I have a secret door, what should the DC for spotting it be? Or picking a lock? Being noticed by an enemy? Let me know if you guys have any helpfull suggestions. Thanks.

[Merlin]

There's a pretty comprehensive list of DCs in the manuals. You can get free copies of the rules here: http://www.opengamingfoundation.org/srd.html