I presume that you will have a separate server for managing the backups and the tape library.
The real answer is that the well-known packages are all good, and they all suck. I am most familiar with Symantec and it is fine. They all have modules available to do backup Windows, Linux and PC's. Be aware that generally speaking, every computer (server or workstation) backed up requires an individual license (like a Windows CAL), and likely will require an agent running on the device itself.
This question has more discussion on the topic of the best network backup software.
Far, far, far more important than the backup software is the diligence and thoroughness of the ongoing backup management. Always remember .. it isn't about doing backups, it is about being able to restore! Make sure that all the meaningful data is backed up, confirm backup success and completeness after every backup, frequently do test restores, create and test server rebuild procedures, manage the inventory of tapes, and keep the tape drive/library patched and running smoothly.