dont go down the text file route - destined for disaster. You need to write the value of the radio to a database field. Then to display the results you count how many results there are in the database and how many of each answser there are (two queries, one which returns all results and one which returns specific results ie "select * from votes where answer = false"). Then you divide the second number by the first, and voila you have a percentage.
If you dont know how to connect your poll to the database then I'd suggest these resources:
ASP tutorials and applications
Kath's Active server pages
ASP from HTML goodies
I'd strongly suggest trying to get to grips with it all from a tutorial than simply waiting for some nice chap (or chapess) to post the answer here - you've a much better chance of really understanding it from a tutorial I would guess - but I'm sure that people will be happy to help if you're having further problems.