To back up over a network all you have to do is map the folders you wish to back up on other machines to drive letters on the machine you will be running the backup on. The software can only back up folders and file on a drive letter, it cannot back up UNC paths like "\\bigcomputer\c_drive".
You can also write the backup to a CD-RW drive on another computer, by sharing that CD-RW drive from the other computer and mapping it to a drive letter on your computer. The only trick is that you won't be able to write the backup to the root folder, because the backup software will not be sure the drive letter doesn't actually map to the root folder of another hard drive somewhere. So you have to add another backup destination, a subfolder of the root folder on the CD-RW drive. You can make the backup to that subfolder just fine.