What doesn't work about the lens? The lens compatability should be 100%, nothing less, with K-mount lenses. I do have one lens that works on my K1000 but not my DL, but that's because it's actually a K/Ricoh mount, and there's a piece of metal that sticks out - I presume it wouldn't mount on any later Pentax film cameras, either. Apparently if you grind down the metal, it'll work fine on the DSLRs, but it's not worth it for a cheap Craig short zoom lens!
Not only should the compatibility be 100%, all the features should work. The only "gotcha" is that lenses without an "A" aperture setting must be used in full manual mode (just as they would on a film camera) and you must hit the A-EL button to stop down the lens if you want it to take a reading. Not such a big deal, and it's tempered by the fact that all manual lenses will still get focus confirmation when you've dialed in the focus right.
Anyway, if something isn't working, that's pretty surprising. It might even be worth asking on one of the Pentax forums, like at Steve's Digicams or DPReview. I don't think I've heard of such an issue before (but I don't spend all my time there, either.)
wkrider, I have the older Pentax *ist DL (I'm holding out for a K10D as my next upgrade) and love the Pentax line. I think the combination of quality and price and features is unbeatable in the current market. On a WDW trip from January, I took over 2,500 photos with mine - there's a link in my signature to my trip report and my gallery, where you can see over 600 photos from the trip (the "worth presenting" ones

at up to 1600x1200 resolution. The sensor is the same as the K100D one and I shot in RAW format for all but a few on-ride photos, so the quality is basically exactly the same as the K100D, only without the IS.