I have the same problem.  I have tried OSs of Vista and XP.  It makes no difference.  The Cisco Version I am using is 5x.  The thing that does seem to be at the heart of the issue is the Internet Service Provider.  I only have trouble with a DSL connection from AT&T.  If I connect the laptop into any other service provider, it is fine.  I also must say that if the DSL was originally with someone else like SBC then merged with AT&T those seem fine too.  It's just the DSL started with AT&T.