I apologize if this is a duplicate question, I know that there are several questions about multiple connection (LAN + LAN and LAN + dialup) but I haven't been able to find one that fits my scenario.

I'm still using Windows XP on my corporate laptop, and I'm connected to the corporate LAN via Ethernet. The LAN NIC has a public IP address, although not accessible externally, obtained via the corporate DNS server. This connection is firewalled and requires a proxy to access Internet.

To access Internet sites blocked by the corporate firewall, I use my smartphone via USB tethering. It is seen as a new LAN interface, and I get a private IP address (class 192.168..).

There are two problems:

1. The LAN is not accessible, as the default gateway goes to the tethering NIC. I'd like to solve this, but I can live with it.

2. My PC becomes unresponsive if I use Windows Explorer to view local files, or even when I open the start menu. I guess that this is caused by attemps to connect to a mapped network drive. But I disabled the "Client for Microsoft Networks" in the tethering NIC. Why the system still hangs? Of course if I disable the Ethernet NIC, Explorer stops hanging.

If you need further details, add a comment. Thanks!