Hi Andreas,
besides Asitic, which you certainly know but does not exactly do what you want, I heard about Veloce RF from Helic (
http://www.helic.com/products.html) which seems to fulfill your needs. It is embedded in the Cadence Virtuoso environement under Solaris, like Agilent RFDE, which may be another (but probably more expensive) option. It just isn't clear why you are looking for a Windows based-tool, as that one could not interact with your Cadence suite running on Solaris...
Hope this helps
Paul