Internet access to workstations

I’m running WinNT 4 w/ SP 4 along with SBS 4.5 which I recently upgraded. I’m using WinGate as a gateway to the internet for my workstations, prior to the upgrade, all the workstations had full access to the internet with no restrictions to any sites or streaming media via real audio, now we can’t access certain sites such as wellsfargo.com. is there something I’m missing, another note, proxy 2.0 wasn’t installed during the upgrade because an error occured. also once i get this going how do i set restrictions to certain sites without any third party software if possible? otherwise are there any recommendations to a third part software.