[CentOS] Problem with large tar file.

I have just completed installing CentOS 4.2 (I came over here from Fedora-Land 
(core-3)). I did this via a fresh install. I tar'd everything to an external 
drive reinstalled the new stuff and everything is working very well. 

I've just got one issue. I have a full system backup Backup.tar that has a 
size of 78,717,880,320. When I issue the command tar -xvf Backup.tar I get 
only about 111MB of data restored. Basically /root and a couple other odd 
things of little consequence.  

I did have a second backup made with cp -pR <stuff> <dest> so I've still got 
my all my stuff from which I can selectivly restore as needed but I'm 
wondering why tar didn't work?  (While being very glad I made two backups.)

Is there a max size limit to a tar file? 
A bug in tar?
Curiosity plagues me.

Thanks for any help.