Cisco Router ISP compatability?

I am planning to create a VPN between two sites in the UK using a CISCO827-4V router and ADSL. I want to ensure the router is compatible with my chosen ISP (Nildram). They are unwilling to confirm if the router is compatible with their ADSL connection or not. I know we use PPPoA in the UK and the router can be configured to use this but are there any other considerations I need to be aware of, or is there anyone using Nildram that can recommend a firewall router to use, (or one to avoid!)