Hard to ask, but I'll try:

Say you have a site with good PR and good inbound links called http://www.gooddomain.com, and on that site you had a page (say named goodpage.html also with decent PR passed from the root domain) and you do a permanent redirect of http://gooddomain.com/goodpage.html to a subdomain of the root named http://goodsubdomain.gooddomain.com.

Will any of the good characteristics and benefits of the original site and page get passed to the subdomain default page?

Will you lose any of the benefits you had by having the the goodpage on the gooddomain?

Somebody out here surely knows the answer to this... don't they?

According to what I have seen and know, Yes.

Just a note of caution. I'm sure the old .html file is part of an internal link structure. If it is then moved to a subdomain that has a different structure it might not do as well. But there is a chance that it will also do better. It's always a gamble.