Will NHibernate 2 and\or Fluent Nhibernate work in a medium trust environment. If not are there any work-arounds?
Not sure about fluent NH - I assume it should - it just translates to XML.
With NH itself you will loose bytecode optimization, all your setters/constructors will need to be public. If you need to use lazy loading you will have to have your proxies generated with build (NH proxy generator).
Should you have some permissions enabled in your medium trust settings you can relax some of the restrictions.