Here is a work around provided by Bill Sanderson about how to remove Windows AntiSpyware from Starting Up with Windows.
Microsoft has a recommended way to do this–see the workaround section of this KB article:
http://support.microsoft.com/kb/892375 End users may be prompted to allow or block administrative actions that originate from a central management tool after they install Windows AntiSpyware (Beta) on a computer that is managed by Systems Management Server 2003
This involves registry editing, I’m afraid. I agree that this isn’t optimal, and I hope that the final product will allow for an easier way to accomplish this.