Here are the 4 Approaches Anshul took when upgrading from MOSS 2007 to SharePoint 2010.
The InPlace upgrade is the easiest way to upgrade from MOSS 2007 to SharePoint 2010. In this approach you will install SharePoint 2010 on the same machine where MOSS 2007 was installed and the Upgrade wizard will upgrade MOSS 2007 to SharePoint 2010.
Database Attach Upgrade
In database attach approach you install the SharePoint Server 2010 on a fresh Machine and you upgrade all the sites from your MOSS 2007 server by detaching the Content databases from MOSS Server and attaching them to the SharePoint 2010 server.
Hybrid Approach 1
In this approach you can make the databases of your MOSS 2007 farm read only and then Install SharePoint 2010 on a different machine. Upgrade your MOSS 2007 farm using the Database Attach approach. (On the new SharePoint 2010 farm) and the redirect your users to the new upgraded farm. This will allow you to give read only access to the users while the farm is being upgraded so it will help you in downtime mitigation.
Hybrid Approach 2
In this approach you can detach your content databases and then do an In-Place upgrade once that is done you can attach the databases using the Database Attach approach. The benefit of this approach is that you can have the speed of the DB Attach upgrade and you can also keep your farm wide settings as you are upgrading the farm by using the In-Place upgrade.
Upgrade Methods in SharePoint 2010: Part 1
Upgrade Methods in SharePoint 2010: Part 2
How To Upgrade to SharePoint 2010 using Database Attach method: Part 1
How To Upgrade to SharePoint 2010 using Database Attach method: Part 2
[courtesty of Anshul Sehgal - http://sharepoint2010blog.blogspot.com/]