TechNet here and here
You must remove the Web servers from service for the duration of the software update process. The reason for doing this is that the software update might make schema changes to the SQL Server database, and user authoring during the upgrade might result in the front-end and back-end servers having different content. The easiest way is to Stop the World Wide Web publishing service (W3SVC) on Web servers to disconnect all the users from the server farm. To stop this service run services.msc and find it in the list and stop it.
Back up the server farm before you start the software update installation. You can use SharePoint Central Admin Full farm backup tool and save to a file share on the SAN if allowed. Or You can just backup the Content databases using SQL Backup. In my mind, Backup is mandatory for production system only because if something goes wrong in DEV and Staging and we have to rebuild, we can get the Production databases to do a rebuild of the farm, it is up to you.
If you customized a predefined site template (aka the 12 hive) by directly modifying the site template files — an action that Microsoft does not recommend — the software update installation might overwrite some of the files that you modified, and your customizations in those files will be lost and sites will break therefore you would reapply any site-template customizations after you install the software update. (sometimes developers or 3rd party tool components alter the 12 hive, I am not sure if you have this situation but we will find out in DEV and staging when we test.
Installing SP3, see steps 1 to 5 below.
Only run the wizard once. Do all these 5 steps on every web server in the Farm, Starting in DEV, make sure you run some tests of a few pages with and without the 3rd party web parts and components installed before moving on to staging, test again in staging and then do production.
Download, Install SP3 and Run wizard in this Order
1. Windows SharePoint Services 3.0 Service Pack 3, 32-bit edition Download
2. Windows SharePoint Services 3.0 Language Pack Service Pack 3, 32-bit edition Download
3. 2007 Microsoft Office servers Service Pack 3, 32-bit edition Download
4. 2007 Microsoft Office servers Language Pack Service Pack 3, 32-bit edition Download
5. Run the SharePoint Products and Technologies Configuration Wizard
To ensure that you have the correct permissions to install the software update and run the SharePoint Products and Technologies Configuration Wizard, Microsoft recommends: That you add the account for the SharePoint Central Administration v3 application pool identity to the Administrators group on each of the local Web servers and application servers and then log on by using that account. These changes are only required for installing the update and then running the SharePoint Products and Technologies Configuration Wizard to complete the upgrade. After you finish installing the update, remove the account on each of the local Web servers and the application servers. In SQL Server, the account must be all of the following: 1. Authorized to access all SharePoint Products and Technologies databases. 2. Granted the Database Creators (dbcreator) fixed server role. 3. Granted the Security Administrators (securityadmin) fixed server role.
Microsoft enforces the installation order of service packs, but does not enforce the installation order of packages or patches. You can install packages or patches in any order you want, so long as every server in your farm is updated to the same level when you are done. In addition, there is no requirement to install an update unless your servers are affected by the problem described in the KB article for the update.
A common question is whether to install the global patch, localized patch, or both.
The decision about which patch to install is based on what you want to accomplish with the installation. The following points provide guidance in making this decision:
- Most of the product updates are contained in global patches. As noted in the product design information, care was taken to separate language-specific parts of the product code, which does not constitute the bulk of the code base.
- There are some code fixes that require both the global and local patch for full implementation. If you install only one of the patches, specific functionality remains broken in the same way that it was before you applied the patch.
- Because a service pack updates everything, the first dependency is introduced at some point after a service pack is applied. This dependency continues to exist until the next service pack. Installing either the global patch or the localized patch does not necessarily affect the overall operation of your server, but if you want to ensure that you have all the fixes, install the global patch and the localized patch.
- Microsoft Customer Support Services (CSS) strongly recommends that you install both patches across your SharePoint environment to ensure that you get the maximum benefit from the fixes and maintain the same software update level across your platform.