Microsoft Access 2003 vs SQL Server 2005 Express There is an Access 2003 database that each "corps" has to manage themselves containing personal, training and material data. It's written very poorly. Besides that, the server only runs Windows 2000, so SQL Server 2005 Express is the highest that it can run. What advantages would I see upgrading it to SQL Server? Speed, reliability and ease of upgrading would be a plus. If it can handle multiple users at the same plus, that'd be the best Plus right now
Few things to consider with using SQL Express vs Access 2003:

SQL Server is limited to 1 CPU
SQL Server is limited to 1 Gig RAM
SQL Server is limited 4 Gig database file (2 Gig on Access)
Creating front end logic for users will take a longer time than Access 2003
Using SQL more reliable as you can do point in time recovery

More comparisons among the two in this link from ZDNET (UK)