I assume your network is a Domain, therefore you will have to join the laptop to this Domain.
Right click on My Computer/Properties. Choose the Computer Name tab. Where it says to join a Domian click on Change. Remove the text from Workgroup and click the Domain button. Enter the name of your Domain, which you will have to find out if you know it. You will then be asked for the Domain Administrator name and password to finsih the process. Hopefully you will be welcomed to the Domain. You may also need to restart at this point.
Write down every original setting before you make these changes should you wish to remove the laptop from the Domain later.
Sorry, but you will also need to set yourself up as a user on the laptop with the same details as on the Server in order to be recognised. You will also need to enter the laptop details onto the 2k3 Server, using the Server Management facility. Basicically this is not much more than the computer name, but you will beasked if you want certain other installations along the way. Just say no. (untick the boxes). If you need help with this please post back. If you are not the network administrator please ask whoever this is to set things up for you. You could end up with an expensive ornanment.
For the above Domain info please read "find out if you don't know it."