|A new router might help I agree, I suspect that your problem is really the point of connection. What I mean is you can only have one of something connected to your ISP. That one thing might be a computer, router, modem.|
As I understand it you are using that adsl just as a hub or switch. It makes your modem share connection, yes, but not in the way you need. The problem might be that your ISP doesn't allow multiple connections. A few ways around that might work. An easy way would be to use Analogx's free proxy to share the "first" computer, (people also in some cases can use ICS, internet connection sharing). Second might be to put the point of connection at the modem if it is advanced enough, then your lan would use private ip's instead of a public IP. Third could be a new router that would allow you to connect to your isp (inside the router) and it then shares the connection on the lan side.
"Best Practices", Event viewer, host file, perfmon, antivirus, anti-spyware, Live CD's, backups, are in my top 10