Will a 580EXII work with a sigma 17-70mm lens normally

Sorry for the dumb newbie question, after it is answered please feel free to delete.

Our nearest camera store isn't very close, and I hate to ask them too many questions if I'm going to buy my flash online.

I have an XTi 400D. I am looking to upgrade both flash and lens. I read something that made me think that perhaps the sigma17-70 lens will not cue the flash properly, so it would be much more troublesome than investing more in the canon lens. Is this correct, or am I misunderstanding how it works?

Sigma and other third party lenses work fine with Canon flash systems.

There are some Canon lenses that report focus distance information to the camera, and this info is used to augment the E-TTL metering with direct flash. The E-TTL system is designed to work fine without this information when the lens in use does not report it.

Thanks a bunch! You saved me a lot of headache trying to find that elsewhere!