Figured it out....In case anyone else needs it:
The login code is found here:
\Inetpub\wwwroot\dotnetnuke\admin\Skins\Login.ascx.vb
On the cmdlogin_click sub I changed:
Response.Redirect(NavigateURL(PortalSettings.HomeTabId, "Logoff"), True)
At the first argument to:
Private Sub cmdLogin_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles cmdLogin.Click
Try
If Request.IsAuthenticated = True Then
If PortalSettings.HomeTabId <> -1 Then
Response.Write("<script language='javascript'> { window.close();}</script>")
Else
Response.Redirect(NavigateURL(PortalSettings.ActiveTab.TabID, "Logoff"), True)
End If
Else
I hope this helps anyone else needing this!