Hi, I'm not sure what this has to do with the Form module, but I'll see if I can help you anyway. The simplest thing I can think of here is to override the style for the Overlay in your own CSS, so that it's set to "display:none" rather than "visibility:hidden". The only reason not to do that is if you explicitly need to use "visibility:hidden" on the Overlay (I'm not sure why YUI made that the default, there are cases where it makes sense but "display:none" seems like it would be the more common use case)
If that doesn't work, you'll likely need to create an extension of Calendar to use in your implementation and override the part adding the style inline that isn't working for you. I haven't mucked about with the inner workings of Calendar, so I don't know how difficult it will be to keep it working and not use that style, but it's worth a shot.
If all else fails, come by #yui on irc.freenode.net on Monday, there's usually a crowd in there (sometime including Allen, the author of Calendar, as well as other members of the core team) who can offer help.
If you run into any Form specific issues, please post those here and I'll offer what help I can.
If that doesn't work, you'll likely need to create an extension of Calendar to use in your implementation and override the part adding the style inline that isn't working for you. I haven't mucked about with the inner workings of Calendar, so I don't know how difficult it will be to keep it working and not use that style, but it's worth a shot.
If all else fails, come by #yui on irc.freenode.net on Monday, there's usually a crowd in there (sometime including Allen, the author of Calendar, as well as other members of the core team) who can offer help.
If you run into any Form specific issues, please post those here and I'll offer what help I can.