I just thought I would run through the process (for my own reference as well) to install SharePoint 2007 on a single box (windows Server 2008 R2 x64) that uses a separate Active Directory server and also has SQL Server 2008 installed (I like to use the full blown SQL Server so I can interrogate the database as I'm working on a data migration project at the moment). In my instance I am setting up a VMWare virtual server.

The process is (such as the prerequisites) as follows:

# Install Windows Server R2 64-bit
# Add the Web Service Role (IIS) using Server Manager > Roles (also tick "ASP.NET" under "Application Development")
# Install updates using Windows Update
# Added the .NET Framework 3.5.1 Features (Server Manager > Features)
# Join to the domain
# Install SQL Server 2008 with (Database Engine Services, Full-Text Search, Client Tools Connectivity, Management Tools - Basic, Management Tools - Complete)

We're then ready to install SharePoint 2007 (which due to compatibility reasons needs to be SharePoint 2007 SP2). You can download this from Microsoft (trial, but just enter an actual key during the install if you have it).

Microsoft Office SharePoint Server 2007 Trial Version
http://www.microsoft.com/downloads/details.aspx?FamilyId=2E6E5A9C-EBF6-4F7F-8467-F4DE6BD6B831&displaylang=en