As it is already mentioned in the above posts that when we have SAV 9.0 and above SEP over installs itself.
Inspite of that if if you want to remove SAV before uninstalling SEP. There ae 4 ways in which you can do it.
1. Removing it from Add remove from all the machine ( This will be very cumbersome )
2.Removing from Cmd line (
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2007091209261948)
3. Running the removal tool ( For that you have contact the Tech Support
4. Runnning the removal script on all the machine at the same time but for that you need altris.
So in my opinion i Will recommned you to use the Migration and Deployment wizrad tp push SEP 11 over SAV 9.0
When you have issues on a had full of machine then you can go for the above removal technique