The first thing to check,do you have an operating network card - does it have drivers? On the Server, click Start, then right-click on the My Computer item and select Properties. On the resultant screen, select the Hardware Tab, then Device Manager. This will show all the components and the state of them, check to see if there is an exclamation mark against your network card entry; if there is, you need a driver for it. All drivers for WHS, should be Server 2003 compatible, so you need to check whats available for your card.
If, after this, you still have problems, let us know and we'll go from there.
HTH,
Colin