Sigma DP2s for Event Photography

Hii all,

I will have to take photos for a big event, indoors, big hall, such as a convention centre.

My concern is the focus in artificial or low light for the Sigma DP2s. What do you recommend? I can use the Flash accessory for more light. Without flash, I wouldn't use more than ISO 400.

If focus is not possible, I found tricky to use the Manual focus with DP2s. If I set the focus to 2 meters, I may get or I may not get the subject in focus. I don't have this problem with DP1.

The subject will be people, so there is no time for trying. It is there a "safe" setting to use? Manual focus to 1.5 - 2 meters? What would you do?

Thank you.