On ESXi you are going to install WIN OS and SEPM is going to interact with Windows. I think it should work fine till you have enough resources...

I have tested SEPm on esxi and Win2K3. It worked fine..(It was only test installation) 

Hi,

      Yes SEP Manager can work with ESX 3.5. However when you configure the policies do remember to convert all policies to non-shared. This helps in reducing the CPU usage by endpoint.

You are really running SEM on Windows, not technically the ESX OS. ESX or ESXi is the host for Windows (or other OSs) virtual machines. SEM doesn't even know about the ESX above Windows because as far as it can tell, it's running on Windows.
We run 28 virtual servers on ESX 3.5 (the heavy-duty version on dedicated host boxes)
No issues with SEM - SEM is installed to server2003 sitting on the ESX hosts.
SEM only knows and sees and feels Windows, not ESX because it's supposed to be transparent. Even ESXi should act the same.
BUT be sure you can give enough resources to SEM! It does need some memory and processor - otherwise it will balk........
The nice thing about the virtual world - you can test with different processor and memory configurations, change it on the fly and never crack a case or lift a screwdriver. And if you take snapshots before making changes, you blow away any VM that breaks and revert to snapshot (at least in our version)
We're looking at using i on our IT notebooks so we can run various configurations, OSs, and such.
We found that one a notebook with only a gig of RAM and a small hard drive, we could actually get Server2008 to launch and run where it otherwise would puke on a real physical box that was that small! ESXi had fooled it very well!
Good luck, let us know how it goes! I guess I'd give it a shot - what is there to lose?

I will be using win2k3 virtual machine on esxi host would that be compatible for my sepm?

thanks for the advise

Check the minimum requirement for SEP..
http://www.symantec.com/en/uk/business/products/sy...

Assign appropriate resources for VM... It will work...

Thanks for clearing it up ANIKET!

i had a successful installation and I'am having no problem thanks