it depends... who'll be affected, workarounds, cost of downtime, and so on... here's the $0.25 version:
1. there should be procedures written for this in your site administration manual that details who you ought to contact and so on...
2. don't have a s.a.m.? now you know why it's important... get with your manager or your client and discuss it with them. then find a sample on the web or in one of the 24seven books or whatever and start writing your tail off...
3. get it approved by the boss/client first...
4. make sure you have a usable backup second... never shut down a produiction server that isn't backed up somewhere... trust me on that but don't ask why... if you need to ask, you don't need to be shutting down servers... ;-)
5. then, if all your duck are lined up, gracefully kick off the users and stop all the applications and databases...
next time you'll be ready.
JTB
Solutions Architect
MCSE-NT4, MCP+I, MCP-W2K, CCNA, CCDA,
CTE, MCIWD, i-Net+, Network+
(MCSA, MCSE-W2K, MCIWA, SCSA, SCNA in progress)