I've covered the setting up of a SharePoint development machine in the past but I thought I might just add a few notes on setting it up on the new Windows Server 2008.
The main difference you'll notice is in the configuration of IIS7. You will need to enable the correct set of features before installing anthing else. You will install the tools in a specific order. The VM I built is a Workgroup machine for development and learning at home, so I can get away with using my MACHINENAME\Administrator account for everything. I am using VMWare Workstation version 6. I use NAT to access the Internet via my host machine.
When installing SQL Server 2005, you can ignore VS 2005-related compatibility errors. However, there is one serious gotcha: you must install the KB 950636 hotfix before installing SQL Server 2005 (only applies to Web Server Edition). If you do not do this, the install will not work on Windows Server 2008. For more details, check Bill Staples' IIS blog.
I created a base VM with just the OS and latest patches. I configured IIS7 and relaxed the browser security settings. I set a maximum size for the VM to grow to dynamically and configured it in 2GB chunks. Then I defragged and ran the VMWare shrink.
At this point, I created a full clone on which I installed the following, in this order:
* KB 950636
* SQL Server 2005
* SQL Server 2005 SP2
* Windows Updates
* VS 2008
* Windows Updates
* Office 2007 Enterprise
* Windows Updates
Finally, install SharePoint Server 2007 with SP1 and you should be good to go :-)