Q: has the old Backup app been replaced by time machine or do I need both

The old Backup app disappeared when Time Machine was first introduced. In OS X Time Machine is the default backup utility. I would suppose you would only need Backup in order to open old backup archives still stored on your computer. However, it may not work if you have a current or recent version of OS X. If you have a PPC, then you still should be able to use Backup.

Perhaps you should first tell us what Mac hardware and OS version are before we tell you what you can toss.