Firefox connects to internet, everything else doesn't...

Ever since I installed Windows 7 Home Premium, firefox works, but no other apps can connect to the internet i.e. online games, itunes, anti-virus, Visual Studio, etc. I've disabled the firewall and anti-virus, but it doesn't help. I'm using a Belkin Wireless N Router and TP-Link TL-WN851N Wireless Adapter. The host uses Vista. The current security settings are: Open Connection with 64-bit WEP Encryption.

My sister has a netbook with Windows 7 Starter on it, but it has no problem.

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