You may try WPF with the powershell wrapper, a quick demo I posted here: Powershell future
Unfortunately I did not find the time to post a complete "how to" yet. Also a little more research needs to be done to make inclusion of these type of dialogs as easy as possible, but I think that's a serious option.
Another option is to recompile one of the fully fledged 32bit GUI active-x controls already there for x64 (if possible - sadly my skills don't allow this).
I think extending DOs dialog scripting is an endless story, there will always be a switch missing once you put in the next feature. That said, I'd like to see positioning and size-options for the basic dialogs as well. o))