Below is a step by step guide that I recently used to migrate MOSS 2007 to Sharepoint 2010.

If you are using MOSS 2007 pre SP2, you will not be able to upgrade directly to 2010. You will need to upgrade your 2007 install first to MOSS 2007 SP2. You can download SP2 install from here: http://www.microsoft.com/downloads/en/details.aspx?FamilyID=b7816d90-5fc6-4347-89b0-a80deb27a082&displaylang=en

Everybody has different methods they prefer for migration, I do not prefer in-place upgrades as it can be risky and time consuming if all fails. The method below involved building a server beside the existing server and a copy of the data is migrated across and upgraded. Once complete you may reconfigure your AAM and network to access the new server.

First you must ensure that you meet the pre-requisites for Sharepoint 2010 (as there is quite a jump). It can only be installed on 2008 R2 64bit servers and even more importantly SQL backend must also be the 64bit R2 version of SQL server. Requirements are as follows:

Sharepoint/Front end servers:

Hardware : 64 bit, 4 cores - 4GB RAM (Developer) 8GB Production - 80GB HDD

Software: The 64-bit edition of Windows Server 2008 Standard, Enterprise, Data Center, or Web Server with SP2, or the 64-bit edition of Windows Server 2008 R2 Standard, Enterprise, Data Center, or Web Server

Database/Back End servers:

Hardware: 64-bit, four cores for small deployments. 64-bit, eight cores for medium deployments - 8 GB for small deployments, 16 GB for large deployments - 80GB HDD (Depends on your data really)

Software: The 64-bit edition of Windows Server 2008 Standard, Enterprise, Data Center, or Web Server with SP2, or the 64-bit edition of Windows Server 2008 R2 Standard, Enterprise, Data Center, or Web Server

The 64-bit edition of Microsoft SQL Server 2008 R2.

Upgrade process:

1. Install your SQL server and Sharepoint server as per usual install procedure.
2. Export your database from your existing SQL database server. I would simply do a full backup of the existing data.
3. On the destination server, do a database restore using the backup file created in step 1. Specify the database name to be WSS_Content (if that is what you are using) and make sure you go to options and tick overwrite existing database (WITH REPLACE).
4. Create a New site in sharepoint Administration Console and delete its existing content database.
5. Open up Sharepoint Management Shell and perform following commands:

   1. "Test-SPContentDatabase – Name WSS_Content -WebApplication http://myapp" - This command will test and verify that your database can in fact be upgraded

   2. "stsadm -o addcontentdb -url http://myapp -databasename WSS_Content" - This command will add the content database and upgrade it to 2010 format

6. Verify that the upgrade was completed successfully by first navigating back to Central Administration / Application Management / Manage content databases, which now displays the upgraded database.

Depending on the size of your database the full upgrade may take a few hours. Even though the admin console may say that it is finished upgrading in the "Check Upgrade Status" page, it may not display on your site for a while. I had to leave my install for a full day before being satisfied with the upgrade.

Once upgraded you will realize that the new look/feel is still the same as MOSS 2007. That is because the UI version needs to be upgraded (for each and every site). To change the look and feel run the following commands in the Sharepoint Management Shell:

$web = Get-SPWeb http://myapp
$web.UIVersion = 4
$web.UIVersionConfigurationEnabled = 0
$web.Update()

Once the above command completes you should now be able to browse your Sharepoint 2010 server with the new look and feel.