It's just not that easy to get a password from NT. Any sensible operatiing system (and we'll include NT here, although loosely) will not provide passwords, but a hash of those passwords. The best you're going to get is the current password hash.
ARS and the Midtier provide no real useful integration tools because Remedy like you to do things "their way", and sadly "their way" is not really compatible with the world today. This is one of the areas that Symbiont have been looking at in great detail.
As for your question regarding the form, I'd personally set the username (on the request header) as a Cookie, and then fetch it again via a javascript RunProcess command. But this is such a good suggestion that we'll (Symbiont) probably end up providing a function for this, as the username is avaialable to the VM through environment variables.
Stan
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Stan Hawkins, Symbiont Solutions
http://www.symbiontsolutions.com