invoke very long calculation process from asp.net

[vytas]

Hello,

I've ran into very interesting task and need some ideas how to implement it. I'm building web app, which has a page for importing data - importing involves very long calculations, which can't be optimized.
I'd like to start some kind of process right after file upload, and redirect user to another page, which shows calculation progress (page will refresh itself using javascript). Question is - what technology should I use? I thought about starting asynchronous webservice, but the question is - will I be able to store reference to that service in session (in order to get progress I need reference to that webservice instance)? Or maybe better idea would be implement windows service, which will be started from asp? Any suggestions welcome,

vytas