Okay, here's what happened, A few days ago, I changed dhcpd.conf (through the template) to use fixed-address on the defined client computers. It looked like everything was working fine until one of the PC's hard disk crashed and I had to do a fresh Win2k install on it. Then suddenly the frech computer cannot browse using IE. Mozilla works and I could also ping the websites on the PC's command line.
Further, other internet access does not seem to work. For example, online games cannot connect and anti-virus updates do not work. When I VPN to the office network, however, it starts working.
Now I removed the fixed-address from dhcpd.conf and restarted, the new PC suddenly works. Could this be a dhcpd issue? I am using SME 5.6 update 5.