Yes you can. I would actually recommend doing it this way as it prevents any conflicts with the DHCP. Most guides on setting static IPs will tell you to put it outside the DHCP range. As long its on the same subnet. If your router was 192.168.1.1 you would want to keep the 192.168.1.X. Im pretty sure changing the subnet can make problems.
To actually do this, go Control Panel, Network Connections, right click on the connection you want to set up and go Properties. Click on TCP/IP, and click on properties.
Change the radio button from Obtain automatically to 'Use the following IP address'. Enter in the IP that you want to use, press tab to go to subnet mask, press tab again and it will auto fill itself. The Default Gateway is the IP of your router, so it knows where the internet can be found. You should set the DNS settings too if you're going to use the internet from the computer.
Thats it, you have now set a static IP!
Edit: This is for Win XP. Vista and 7 are slightly different, but same priciple and options.