You can rule out the Vodafone card - it's a modem device (listed in Control Panel > Phone and Modem Options > Modems). Mine causes no issues with wi-fi.
What's being listed as your preferred network? Control Panel > Internet Options > Connections.
By the way; are these wireless networks yours, or ones that are provided for open access? If they are privately owned - at neighbour's properties for example - then the amendments to the Wireless Act prohibit you from even accessing them.