Documenting sculpture isn't all that much about the camera. Any ILC on the market today is more than capable of doing it. Your decade old Pentax K10D should be able as well. It's not that much about the lens, either, as long as you're using something reasonably sharp. At the apertures you're probably going to want to use, anything that's not misaligned or otherwise out of whack will be sharp at f/5.6-f/8-f/11. The 18-55mm kit lens that came with the K10D is probably sufficient unless you're wanting to display at very large sizes.

Documenting sculpture is all about lighting and technique.

As far as technique goes, one would assume you're going to have the camera on a tripod and release the shutter with a remote cable or wireless remote. If the K10D offers mirror lockup, that would help improve your results as well.

As far as lighting goes, what you need all depends upon how you want to present your work. Without knowing how large your sculptures are as well as a few example photographs that show us what you want the photos of your work to look like, it's hard to give much guidance about lighting your project to get a specific look.