Microsoft released the SharePoint Server 2010 beta recently.
Also Microsoft states that migration process from SharePoint 2007 to
2010 is fairly easy and straightforward, however as far as my knowledge
goes migration process from SharePoint 2003 to 2007 is difficult and
painful with several incompatible elements to be dealt with.
The SharePoint 2007 site presented in this blog is using Windows
Server 2008 R2 64-bit (which is minimum requirement for SharePoint 2010)
with SQL Server 2008 Express Edition 64-bit as underlying operating
system and database.
First, let's look at the SharePoint 2007 site we migrate. For this
demonstration I created a simple MOSS 2007 Enterprise environment based
on the Collaboration template, which contains some generic web parts
we'll test on SharePoint 2010, Document Center and Search Center. I
setup and double checked the search, because I wonder if the migrated
SharePoint would be able to use the search database crawled in the
previous, 2007 version of SharePoint. Search is an important issue for
migrating SharePoint installations with large amount of data where a
full crawl of the content may take weeks.

My Intranet Site in MOSS 2007
Now, install SharePoint Server 2010 right on the existing
installation. In the Setup window, we can view the server requirements,
installation guide etc. We will skip this part and proceed straight to
the Installation.

SharePoint Server 2010
installation screen
First we need to install software prerequisites. We may already have
all required components since we are already running MOSS 2007, but to
be sure, we'll go select this option.
The preparation tool window that launches checks our server for the
required components, and installs them if needed. The components that
will be updated are:
- Application Server Role and IIS Role
- SQL Server 2008 Native Client
- Microsoft "Geneva" Framework Runtime
- Microsoft Sync Framework Runtime v1.0
- Microsoft Chart Controls for Microsoft .NET Framework 3.5
- Microsoft Filter Pack 2.0
- Microsoft SQL Server 2008 Analysis Services ADOMD.NET
Let's open the preparation tool. After reading the short tool
description and accepting the terms, the preparation tool will start
updating the server immediately.

SharePoint Server 2010 Preparation Tool
After successful configuration, the summary screen will be displayed
and the tool will likely request a reboot of the system.

Preparation Tool Summary Screen
When Finish button is clicked the system will reboot
automatically. After the reboot, the Preparation Tool launches again and
finishes the rest of the steps. Now our system is ready to install
SharePoint Server 2010, so select that option from the setup pane.
We will be prompted to enter the license key (which is necessary even
when SharePoint 2010 is in Beta):

Product Key window
in SharePoint Server 2010 Setup
After the key we have to read and accept license terms. Next screen
advise that MOSS 2007 was detected.

SharePoint Server
2010 Setup Screen - Upgrade Window
As advised in the above screen we need to run the stsadm command now
to ensure our intranet can be successfully migrated. Open cmd.exe
console in administrator mode.

Start - Cmd.exe in Administrator mode
Navigate to the MOSS 2007 Bin Directory, which is located by default
at C:\Program Files\Common Files\Microsoft Shared\Web Server
Extensions\12\bin directory.

Cmd Window in the MOSS 2007 bin folder
Enter stsadm -o preupgradecheck. This command does not
perform any repairs, but \only checks for and reports issues with
possible solutions to apply before the migration. As the command
executes we will see the output continuously displayed on the screen
with different status notifications. In this check, some notifications
were "Aborted due to internal error". We will ignore this for now as the
overall check was successful.

stsadm preupgradecheck output
The browser will then open to display the html document with the
summary of the output and details of every issue. As all components
passed the test we are ready for the migration.
Go back to our SharePoint Server 2010 Setup window and click the
Install Now button.
After the installation, we'll see the final screen where we are
informed that we must launch the SharePoint configuration wizard in
order to update our content to latest SharePoint version.

SharePoint Server
2010 Installation Summary screen
Click Close to run SharePoint Configuration wizard. If you were
expecting a wizard similar to the SharePoint 2007 wizard, you will
be disappointed . We have now entirely new environment for Sharepoint
2010 version and hence a new Configuration Wizard.

SharePoint 2010 Configuration Wizard
Click Next, and the below warning will be shown:

Warning
Window in SharePoint 2010 Configuration Wizard
Click Yes and we will see a new feature of Sharepoint 2010 - Farm
Passphrase.

Farm Security Settings Window
The Farm Passphrase will prevent server administrators from changing
any data in our SharePoint 2010 installation when no password is
provided. Administrations won't be able to use content or configuration
databases even if full database backups are obtained. Enter a password
and continue with the configuration.
The next step is the Visual Upgrade.

Visual Upgrade Window
Here we decide the look and feel of the SharePoint site. You can
upgrade all your farm to the SharePoint 2010 design right now. However
we will not do this in this demonstration in order to be sure that
everything will run fine in 2010 before modifying the design. SharePoint
Server 2010 allow me to preview the look and feel of sites before
switching to the new SharePoint design, so select "Preserve the look
and feel of existing SharePoint sites" option, which will maintain the
original SharePoint Server 2007 design.