Microsoft strongly recommends installing the SP1 before you install the Infrastructure Update. In my opinion you should have done so much earlier, if your SharePoint Farm is still running RTM!
- Acknowledge the license to install the update
- The SharePoint Configuration Wizard will start automatically after the update has been installed
Well, updating your farm is like installing a regular hot fix. Nothing more.
If you are running MOSS, you will get new features with the update:
Key updates for SharePoint Server 2007 include:
- New Search features such as federated search and a unified search administration dashboard.
- Several core fixes to Search to improve performance and scale.
- Platform performance improvements and fixes.
- Several core fixes to the publishing Content Deployment features to improve reliability.