For my environment, our org charts are on our intranet (I'm guessing this would be fairly common, since org charts don't have a whole lot of value to external customers)... so we have a little more control over the client environment... but because a large base of our employees (engineers) are UNIX-based, we do still need to support Netscape 4.7x. And we could only use Flash v.4, v.5 at best.
Prefer as little javascript as possible... since we're finding that engineers, as a whole, will turn javascript off more often than not (same with cookies). Java is a possibility... though, again Sun-based rather than MS. Straight HTML or dynamic graphics would be the ultimate.
We run ColdFusion 5.0 and MX Enterprise servers, on Solaris (so no DLLs or C++ CFX's) and Win2KPro.
When I was in planning, before I postponed the project, I was figuring to keep the chart at around 680-700pixels wide. It would show two to three levels of hierarchy, and then the names would be links to allow the user to drill down to subsequent levels.
I was looking at doing the whole thing with a dynamically-derived table... with colored cells for people, and graphics for connecting lines. But then things like dotted lines, that didn't necessarily connect to someone directly underneath a given manager, started to become a problem that made my brain start to hurt.
Hope it helps,
-Carl