first, WindowsIdentity.GetCurrent has an overload that you can use to determine
if you are currently impersonating.

then you can undo impersonation temporarily to get to the process account

do this

using (WindowsIdentity.Impersonate(IntPtr.Zero))
{
 string process = WindowsIdentity.GetCurrent();
}

from the docs:
"Calling the Impersonate(IntPtr) method with a userToken value of Zero is
equivalent to calling the Win32 RevertToSelf function. If another user is
currently being impersonated, control reverts to the original user."

-----
Dominick Baier (http://www.leastprivilege.com)

Developing More Secure Microsoft ASP.NET 2.0 Applications (http://www.microsoft.com/mspress/books/9989.asp)