I sold a good friend of mine a original ( non HSM) SSigma 70-210 a couple of years ago. Wouldn't work on his 10D. He sent it back to Sigma - they re-chipped it. Works fine on his 10D and is  WAY faster in terms of auto-focus speed compared to the original pre-chip change unit.
  recently e-mailed Sigma wondering if they still offered this service. Their responce was that they need to know the specific model of lense - since they do not have chips available for all older AF lenses. Have only owned a couple of their lenses - but they seem to be at least OK  - in many cases better than the bottom of the line ( and more expensive) canon lenses. the damm L lenses are a whole nother thing - really great optically - but I think the L stands for Lug? I wish Canon would discover platics for L lenses - the weight of these things is a boon to the chiropractic profession.

Does anyone know is it possible to use older non-Canon marque lenses on digital bodies (350 D?)I specifically mean "older " generation lenses...as I obviously understand you can use new canon fit lenses...but I wanted to buy a s/h sigma APO zoom off Ebay, but I have heard that there can be a problem when using on digital bodies?

>> they do not have chips available for all older AF lenses

That is exactly why I think it's not a good idea to buy old Sigma lenses. Also, re-chipping is not free in all countries (e.g. in Israel it is ~70$-100$, depending on lens). Check with your local importer.

Happy shooting,
Yakim.