How to assign a specific PC a static IP on a network

We have Windstream DSL in a small office. We have two static IP addresses from them, and I need to assign it to a specific Windows XP computer on my network.

How would I go about doing this? The intent is to have a company in Texas access it via Remote Desktop Connection.

DSL Modem > Apple Time Capsule Router > Linksys Switch > Windows XP Computer.

Note that all the other computers are also plugged into the Linksys switch. But I need the one computer to be assigned it’s own IP address.

Any help would be greatly appreciated.