When using Web GAteway 6.8.7 when opening multible tabs on IE 7 sometimes hang and you need to close the exploorer and reopen to solve the issue and be able to browse.
is the behaviour the same in case you don't have proxies configured?
As a quick thought out of what I experienced - try disabling all the "Windows Live" plug-ins (Tools->Internet Options->Programs(Tab)->Manage Add Ons). They usually product requests on every new tab (for whatever reason) and the tab won't open until the response is back.
worth a try.