This policy setting allows you to specify a list of web sites that will be allowed to open pop-up windows regardless of the Internet Explorer process's Pop-Up Blocker settings.If you enable this policy setting you can enter a list of sites which will be allowed to open pop-up windows regardless of user settings. Only the domain name is allowed so www.contoso.com is valid but not http://www.contoso.com. Wildcards are allowed so *.contoso.com is also valid.If you disable this or do not configure this policy setting you will not be able to provide a default Pop-up Blocker exception list.Note: You can disable users from adding or removing websites to the exception list by enabling "Turn off Managing Pop-up Allow list" policy.
Windows Components\Internet Explorer
At least Internet Explorer 6.0 in Windows XP with Service Pack 2 or Windows Server 2003 with Service Pack 1
HKLM\Software\Policies\Microsoft\Internet Explorer\New Windows!ListBox_Support_Allow; HKLM\Software\Policies\Microsoft\Internet Explorer\New Windows\Allow