PPPoE is the abbreviation for Point-to-Point Protocol over Ethernet. PPPoE is the protocol that your ISP uses to transmit information to and from a computer. Some DSL-based ISPs may not call PPPoE by name, but this information is relevant if you use a DSL modem and are required provide a user name and password in order to connect to the Internet.
The Startup Disk preference pane is simply filtering out (that is, not displaying) any mounted volumes that it doesn't consider bootable. Its definition of a Boot Camp volume includes that the mounted volume either be of type msdos or ntfs--this is hardcoded into the preference pane plugin. This doesn't mean your Boot Camp volume has become unbootable. It's merely not showing up in the GUI. You can hold the opt key during startup and choose the Windows partition to boot from. You can also remount it (read-only) using the NTFS file system built into Mac OS X and it should start showing up in Startup Disk.
Mac OS X is a Unix-like operating system developed by Apple for their Mac hardware line.
Windows is a series of operating systems, running their own proprietary kernel, that is developed by Microsoft and licensed to various computer manufacturers.
You do not need connection software when using Mac OS X, so this does not affect you. Most ISPs only require the correct user name and password when your computer connects to their service. Mac OS X can do this without any additional software. Follow the instructions in technical document 106282: "Mac OS X 10.0: Setup Assistant Does Not Accommodate DSL User Name and Password
Mac OS X 10.3 works with these Macintosh computers:
* Power Mac G5--all models except Power Mac G5 (Early 2005), Power Mac G5 (Late 2005) which use Mac OS X 10.4
* Power Mac G4 or Macintosh Server G4--all models
* Power Macintosh G3 or Macintosh Server G3 that have built-in USB ports
* iMac--all models released in 2004 or earlier
* iBook--all models except iBook G4 (Mid 2005) which uses Mac OS X 10.4
* PowerBook G4--all models except PowerBook G4 (Double-Layer SD) which uses Mac OS X 10.4
* PowerBook G3--Bronze Keyboard models only