there is a bug in gzip when using IE6, so gzip should be turned off when it is being requested by IE6. unfortunately, IIS7 compression module doesn't handle this. There is a work around using iis url rewrite module. http://www.andornot.com/blog/post/IE6-gzip-bug-solved-using-IIS7s-URL-Rewrite-Module.aspx

http://support.microsoft.com/kb/837251