Setting multiple default home page in IE7

I can set the home page for all users using mmc and group policy with no
problem. Is there any way to set it for a second tab in IE7? I tried setting
up the two lines for the two URLs in IE7 settings homepage then copy and
pasting into the line in the URL field in Group Policy but that doesn't work.
Thanks for any help in advance. Also how do I lock this so it can not be
changed?
Jon