You shouldn't really notice any significant difference.
Be glad to help out however I can.
I believe that SBC requires PPPoE, and thus you would need to log on with your username and password. At least that's how the dynamic IP setup is with my friend's computer.
Either use the software they provide, configure your computer to automatically transmit that information (some do, I'm not sure about all OS'), or get a $50 NAT router/firewall (i.e. a Linksys router) that will do it automatically.
I believe so.
I believe SBC only assigns new IP addresses whenever you log off and back on again.
I believe that Windows XP Pro can do it, but I'm not 100% sure -- I'm a Mac user.
That said, having a Windows machine directly connected to the internet is an Extremely Unwise Idea(tm), what with the large number of viruses, worms, and other vulnerabilities inherent in Windows. A $50 NAT box would serve you well.
I suspect that it will work nearly as transparently as it does right now, even more so if you get a NAT box to automatically enter the login/password whenever you use your network connection. If you're not presently logged onto SBC's network, it may take up to five seconds or so to log on, after which there should be no delays until the connection is idle for long enough to disconnect.
Cheers!