Microsoft Office Sharepoint Server Service Pack 2 includes the infrastructure update.

Here is the proof:

“ SP2 includes Service Pack 1 and all the major updates since the release of Windows SharePoint Services 3.0 and Office SharePoint Server 2007.”

http://technet.microsoft.com/en-us/office/sharepointserver/bb735839.aspx

So if you are on SP1 and planning for an update, you dont have to apply infrastructure update prior to SP2. it already has it!

SP2 installation steps:

Installation Steps

1. Service Pack 2 for Windows SharePoint Services 3.0 ink
2. Service Pack 2 for Windows SharePoint Services 3.0 Language Pack (if applicable) Link
3. Service Pack 2 for Office SharePoint Server 2007 Link
4. Service Pack 2 for Office SharePoint Server 2007 Language Pack (if applicable) Link

good luck!