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#11
Go to Start > Control Panel. Click on Network and Sharing Center. Click Change Adapter Settings (on the left hand bar). Right click Local Area Connection and click Properties. Highlight Internet Protocol Version 4 (TCP/IPv4) and click Properties.
Click "Use the following IP address:" and fill in the fields based on your router's settings. You can look at roommates settings for this information. Use the same subnet mask and default gateway as them, just use a different IP. For example, if your roommates have the IPs 192.168.1.100 and .101, use .110 just to be safe.
For primary DNS, you should be able to use the same address as the default gateway.