1) The JDE MTRs (Minimum Technical Requirements) do not list SQL 2005 on Windows 2008 as a supported combination. They also do not list SQL 2008 on Windows 2003 as a supported combination. Fortunately, upgrading the database itself from SQL 2005 to SQL 2008 is not a hard process.
2) If you plan to upgrade the database, then upgrading the Tools Release will be a required step, since SQL 2008 is not supported until 8.98.1 or higher (the current release is 8.98.3.4). If you upgrade to this Tools Release level, then you have several ESUs you will also need to apply, and it will most definitely require that you apply the Tools Release to your Deployment Server and JAS server(s).
This will affect your web clients, since they will be required to update their ActiveX controls (if using IE), and there will likely be some registry changes you will have to perform to get them to use the new HTML client.
Also, since the web server requirements have changed, I would expect that you would have to install a new version of WebSphere or Oracle Application Server, or move to WebLogic.
3) So, while your initial desire is to move to a new Enterprise Server with updated database, you will have to go at it from the other direction and make sure you have everything for the new Tools Release running first.
To help with your research, read through the JDE MTRs here:
link.
P.S. Hopefully, you can see from these points why ebearman is recommending that you find someone with the requisite skills to handle these tasks.