Moving from one location to other

My company is moving its office. We have only 49 employees. The network is NT 4.0. ONE PDC that have a Webserver, MS Exchange server 5.5, Proxy server 2.0. Cisco 1700 to connect to the SWB ISP. All the workstaations are Windows 98 and Windows 2000. Like to get suggestion about what would be the best way to move the network and the workstations. Downtime needs to be very minimal because company works on mission critical software development.