Dear Peace-Warrior,
Compatibility between body and lens implies two standards:
- mount of the body
- mount of the lens.
As I learned from the other post, you are planning to buy a K10D, so the Sigma should be Pentax-compatible, with the mount K.
On the body side
The
fact-sheet of the K10D specifies
Quote:
Lens Mount:
- PENTAX KAF2 mount compatible with PENTAX KAF2, KAF and KA mount lenses
- Power zoom function not available
- K-mount lenses usable with restrictions
- S-mount lenses usable with adapter and with restrictions
- 67/645 lenses usable with adapter and with restrictions
On the lens sideThe
Sigma macro 70mm F2.8 EX DG comes in various flavours
Quote:
Corresponding AF Mounts SIGMA, CANON, NIKON (D), SONY, PENTAX
Be careful: this is the latest revision from Sigma. Check the mount of the proposed 70mm lens, that may differ.
70mm gives 105mm in digital world, so it is a small tele, suitable for portraits.
A couple of suggestions
May I do a couple of suggestions?
First, the K10D is an excellent camera (
Disclaimer: I own one 
) and, since it is aimed at prosumer / professional, implies a learning curve: see my
review and the discoveries I made. For example, compared with other cameras, there are no special modes, as portrait, landscape and so on: such modes (actually, I've never used) prevent you from being free to find the perfect adjustment.
Second, select both the kind of pictures you want to start with (portrait, lanscape, sport) and the available budget to make your selection easier.
Another couple of suggestions
As a matter of fact, the K10D could come bundled with lens at a very aggressive price. The body only is USD 660 and the body + 18-55mm bundle at USD 730, or USD 70 only for the lens.
On top of that, special holidays season rebates are available, see
http://www.pentaximaging.com/purchase/rebates_offers/
Enjoy

_________________
--- rei_vilo
Pentax K-5 + BG4 + DA* 16-50 + DA* 50-135 + DA* 60-250 + AF-540FGZ
reivilophotography.weebly.com