You may go through the following links:
...sorry? ESX 4.1 isn't supported? That's because it is vSphere 4.1 which IS supported if you took the time to dig down to pg. 9 of the SCL. It also clearly states you need BE 2010 R2 to support it.
Please take the time to research CAREFULLY before posting incorrect details. The poster is quite capable of backing up his VM environment, provided he has BE 2010 R2!
EDIT: Meant 4.1, not 5.1!!! Thanks for the correction pkh!
First upgrade your BE to 2010 R2.
Then you can use VMware Virtual Infrastructure Agent to backup your ESX server.
For more information on VMware agent go through the admin guide. (Page no 1337)