Before you proceed, ensure that you have a second working domain controller that's a global catalog and DNS server. Ensure replication is working, etc. Move FSMO roles from your DC that you plan on rebuilding to the second DC. If the domain is functioning properly, ensure full backups are done and then use dcpromo to remove active directory from the DC you want to rebuild. Delete DNS records if necessary. This takes care of active directory.
Record all OS settings, printer share names, VPN settings, etc. etc. Use things like "net share" to quickly get a list of shared folders. Backup data and move to a temporary location. Delete the computer account, and ensure that there are NO references to the server in AD, DNS, etc. etc. Very important that this is done.
Reinstall and configure Windows. If necessary, think about logical drive configuration, as it's a good opportunity to clean up if necessary. Best practice is to keep data on a separate partition from the OS....also makes it easier to reinstall Windows, etc. Restore all of your data, and test everything. Join to the domain using the same netbios name, and IP address.
Reinstall AD on the rebuilt server, make it a GC and DNS server if necessary. Some people recommend not reusing netbios names of servers, but I find that as long as you take care of your AD environment and keep it clean, it shouldn't be a problem.
