Thanks Matt. I uploaded a sample to my site for anyone who's interested to see exactly what I'm referring to.
http://www.sticksandstonesphotography.com/temp/banding.jpg
FYI - On the DPReview forum, they were talking about banding of a different sort that can occur when firing off multiple shots quickly. It does it on mine, tho I'm not too concerned as I don't shoot too many action shots. Here's a sample:
http://www.sticksandstonesphotography.com/temp/banding_experiment.jpg

Hi --
Wondering if anyone knows of a possible cause of this problem.
A few weeks ago, in the middle of shooting a dance competition, a series of 7 or 8 pictures had this horizontal band. The problem went away and hasn't returned in the 800 pics I've taken since. The first pic was all messed up and pixelated, then the following 6 or 7 pics had a horizontal band across the top. Looking at them on the computer, it seems that part of the image from the previous frame is in the band. I talked to Pentax, who was helpful, but they didn't have any answers. They suggested formatting the SD cards and removing the batteries for two days to completely wipe out the memory and reset everything in the camera. I haven't had a chance yet to leave it batteryless for 48 hours, but the problem hasn't come back, so I'm thinking it was a one-time fluke. The few knowledgeable folks I've talked to seem to think it's the camera and not the SD card, and also it's a possible power (battery) problem. I was using a Sigma flash, EF-500ST, if that means anything.
I'd attach a sample picture, but I'm new to this forum stuff and don't know how to do that.
Any feedback is appreciated.

No one is sure of the problem, but this thread on the DPReview forum may help.
http://forums.dpreview.com/forums/readflat.asp?forum=1036&thread=15533251&am...
It happens on my DS as well, so you're not alone.

Check here for sample pics:
http://www.pbase.com/cameras/pentax