VB / C# advice needed

After developing in the LAMP environment for past 7 years, I'm now working in a Windows shop (Win Server 2003) and have inherited an intranet written in VB Script. I confess I'm pretty clueless with the whole deal so far, I have successfully fiddled here and there but don't really understand the "big picture".

I need to learn a Windows scripting language quick, so I'm wondering if C# can these days be used to entirely replace VB script in .NET web development?
In other words, is C# a "drop-in" replacement for VB?
Does the .NET environment transparently handle whatever run-time compilation is required?
Can C# also be used for sysadmin scripting, eg. login scripts etc?

Thanks