It's a beta. On some systems, it causes problems--not necessarily
specifically with Norton Internet Security.
You could install it, use it to check whether your system needs its help in
cleaning, and elect not to use that help, and uninstall it, and there should
be no effects on your system from that test.
Or, you could wait until it is a supported product, and see whether either
vendor has a statement about compatibility to make.
My own perspective would be that you would be better off learning more about
whatever issue you found between Service Pack 2 and NIS, and finding out how
to fix that. That's more basic to the security of your system than adding
Microsoft Antispyware.