having a similar problem
I've got a similar problem. I set up Parallels at home, when connected to my wireless network. Everything works fine - both Mac and Parallels can get out onto the Internet. But if I move onto a different network - say, for example, the hotspot at the local Starbucks - things fall apart. The Mac can talk on the network fine (once I go through the starbucks login page), but the virtual machine doesn't even get as far as the login page - I get the dreaded "this page cannot be displayed" error.
So I decided to play around with the command line. I check my IP address with "ipconfig" and noticed that it still had the IP that my DHCp server at home assigned to it. So I did a release/renew cycle (ipconfig /release, followed by ipconfig /renew) to get a new IP address, and I am now assigned an IP address on the starbucks network. However, I still cannot open the login page, getting the same "this page cannot be displayed" error in IE.
Is there any way of getting this to work?