Problem with ISAPI filter ?

I am facing one problem regarding the ISAPI web filter. I have a web filter program which passes user requests and responses to my engine (dll) for processing. My application is multi-threaded and uses the threads provided by IIS server. As I am using IIS threads for further resource access such as registry its failing as its not having sufficient security credentials.
For the same reason I wanted to switch the security context of the thread before calling into the engine and revert back after the work is done.

How can I achieve that ? My app runs on W2K, IIS 5.0 (medium setting) with MS proxy server.

any feedback is appreciated.

Thanks,
Dhiraj

P.S. As per the comment from Microsoft they say you can call ReverToSelf before creating any worker threads ???