The following docs provide step-by-step instructions:
<a href=”http://technet.microsoft.com/en-us/library/bb125110(EXCHG.65).aspx”>How to Uninstall Exchange Server 2003</a>
<a href=”http://support.microsoft.com/kb/833396″>KB 833396 </a>How to remove Exchange Server 2003 from your computer
If the server you are removing was the first Exchange 2003 server in the Administrative Group, there are some additional considerations and steps to take, discussed in the following KBA:
<a href=”http://support.microsoft.com/kb/822931″>KB 822931</a> How to remove the first Exchange Server 2003 computer from the administrative group
Additionally, if the server receives inbound internet mail/is target of any MX records, you will need to remove or modify these MX records (either point them to another server or remove). Similarly, any firewall rules to allow inbound/outbound SMTP (or other -> HTTP/IMAP/POP… ) traffic will need to be modified or removed.