You mention that ntl ip addresses are dynamic but in my experience they are not. I have a STB and the ip address that I have now I have had for several months now. I don't know if it is different with a SACM.
I think RemotelyAnywhere from
http://www.remotelyanywhere.com/ should cover both points. I have used versions 4 & 5 in the past before moving onto Remote Admin from
http://www.radmin.com/ and RemotelyAnywhere allows you to access and administer your server from the web. It's pretty nifty and will tell you everything you need to know about how your server status, it's worth a look.
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here's a screen print
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