iusethis is a great website with software that other people have recomended. NetNewsWire is a good RSS reader, Adium is a good free instant messanger that supports loads of protocols.
You will have to encode the DVD into a file that iMovie can read, I recommend Handbrake Once you create that file just drag it into iMovie. I hope this helps
Did you download the one for your version of Mac OS X? On your OS installation disc, click optional installs, and install X11 from there. No need to reinstall the OS