Chuck, the IDPA web site here: http://members.idpa.com/Content/Rules/x2gukat1.wyt.pdf has the rules. Holsters are under equipment section 08 starting on page 30 something. IWB holsters can be used, but are not required. I use a regular hip holster. No pocket holsters allowed.

Well, I do shoot AT the 25 yard targets although I could have sworn that I was shooting blanks with the longer shots with the Bug at last Saturday's match. The very short barreled things have plenty of inherent accuracy but that short sight radius makes you really have to hold 'em and squeeze 'em for a chance at a good 25 yard hit.
Scott