What you describe, grabbing http://visibletweets.com/
is not really what's talked about here. Streaming video is different from grabbing something from a web browser on the same computer.
If you want to stream from an IP cam you can use IPCAM to Syphon to get the camera straight into MadMapper. But if you need more textures you might want to bring it into Modul8 first which is possible with some tricks. Search the forum for Syphon input.
As for getting the tweets http://visibletweets.com
you can either use CamTwist but you can also use a Syphon screen grabber wich will give you better image quality. Again: google for Syphon input in the forums if you want to use it in Modul8. Other VJ apps like VDMX has built in functions for grabbing screens from other apps.