I don't know whether there would be any problems installing this on an SBS 2008 server. You can try it and see. If it installs properly, you should be able to use the AD module commands from your Windows 7 computer.
If the AD Management Gateway Service won't install on SBS, then I'm afraid you're out of luck, as far as the Microsoft ActiveDirectory module is concerned. You could download the Quest AD cmdlets, though; they're very similar to the AD module, but they use LDAP to communicate with the DCs, instead of relying on AD Web Services. http://www.quest.com/powershell/activeroles-server.aspx
You can also use the underlying .NET System.DirectoryServices classes yourself, but it's not as user-friendly.