ok, so I think I have it cracked and the solution was kind of staring me in the face...
These instructions are for Mac OS X users
Download Nicecast http://www.rogueamoeba.com/nicecast/
It's free to download & test out but after 20 mins or so, 'noise' gets overlaid on the broadcast so it will set you back $40 to use a fully functional version.
It's a simple .dmg app. Install & open it up, making sure you have the Broadcast & Server windows showing.
Broadcast first: Hit the Source button and select your source, which will be Safari or Firefox depending on which browser you use. You can leave the advanced button alone.
Go into Quality and choose Custom from the preset option. Set the bitrate to 320, Sample rate to 48.000khz and Channels to Stereo.
To the Server window:
Choose Built-in Server (the only option when you first start Nicecast)
Make sure the button on the right of the window says Stop. Then uncheck the Address option in the Network area and enter your computer's IP address ie. 192.168.x.x The port should be set to either 8000 or 8100.
In access control set the number of users to 1 (assuming your broadcasting to 1 roku unit)
Using the built-in server you shouldn't need to specify a Name & Password in access control, but to be sure you can eneter that information. You should be able to do this either in boxes in access control or do it through the .plist file. If for some reason you have problems entering the password in the interface you can find the .plist file is /yourusername/Library/Prefs and the file is called 'com.rogueamoeba.nicecast.plist'. Open it up and scroll down to the line with OwnerPassword. Double click in the 'Value' column and enter your desired password. Hit return, quit out and save if it asks you to.
Now bring up the Roku's control page via Bookmarks/Bonjour in your browser and go into the Presets page. Choose yourself an unused preset and enter the following info in the url box:
(where x is of course the IP address of your mac)
Now you need to go into System Preferences and open up that 8000 or 8100 port you specified in the server setup. So,, System Prefs>Sharing>Firewall>New
In Port name, scroll down to Other and choose that. In TCP port, put in that 8000 or 8100 number you chose. UDP leave blank and then give it a name ie. Pandora. OK that and quit System Prefs.
you should now be ready to broadcast to your SB. Bring up Pandora and start that playing through your web browser. Go back to Nicecast and in the Server window hit the Start button. The status should change to Active. Go to the Broadcast window and hit the Start Broadcast button. The state should change to On Air and you'll see the peak meter spring into life. Head to your SB and browse to the Pandora preset in Internet Radio and all things being well, you should be in business.
If for any reason you get a connection error message in the broadcast window, hit the Share button and you'll see the address you're broadcasting on. The 'internet' and 'local' addresses should be the same, and correspond with what you enetered in the Preset url box in the Roku Presets page.
G5, OS X 10.5.8, 3 x M1000, iTunes 10.4, slimserver 6.2.1/alienbbc (now redundant), firefly svn 1586, uNSLUng 6.8