I don't really have a true macro lens. The one I shot this week's photo with is a 70-210 f4 SMC A. It's 30 years old or so, and it has macro at the 70mm end. I can focus as close as ~10 inches maybe? 1:3 magnification if I recall correctly. It's a stellar fucking lens though.
I'd try to find a 100mm 'Dental' macro on ebay for true macro capability on the Pentax.
actually, more on a serious note. if you're looking into the 40D but want something a little more powerful...the 5D's are currently selling for $2200 (about $700 more than a 40D) at BH. the MarkII is about to hit the street so they are trying to get rid of all the 5D models.