Recently I was thinking of a similar problem, and the basic problem is that webinterfaces are not very well suited for this kind of action.
You could use flash or java to make something better suited, but that's a lot of hazzle. Most ideal would be a desktop application. But that does not fit in well with the webbased application idea.
The direction I'm now thinking in is the use of 'starkits' - gives you the benefit of both worlds:
a) not being hindered by the inherent limitations of webpages (it's just a normal windows/x-windows application)
b) almost as easy to use as a regular webpage (for the user)
The idea then is:
- the user has downloaded a suitable TclKit for his platform (1mb download, just once)
- and when he clicks on the link to e.g. edit the gantchart, he gets downloaded a suitable starkit (instead of an HTML page). The kit is probably around the same size as a page with images. After editing (no roundtrips to the server!) the kit uploads the edited chart back to the server and terminates.
I haven't done anything in this direction yet, but I thought it may be worthwhile sharing the thought.
In case you're never heard of tclkit/starkits:
- about starkits: http://www.equi4.com/starkit.html
- about tclkit: http://www.equi4.com/tclkit.html
- the starkit archive: http://mini.net/sdarchive
