I had worked sometime on an application in which we had to convert a MS Access database to SQL 2005 and 2008. I would rather say it was migration than conversion. MS access comes with an inbuilt option to migrate to any SQL Server 2005 Database but it does not create any relationship and indexes has to recreated again. This is annoying if you have too many of them.

Hunting around I found the official page of Microsoft where the official tool for Migrating MS access, Oracle and Sybase databases to SQL sever 2005 is listed. This too is called as Server Migration Assistant ( SSMA). Here is the list from the official page

• Gain access to SQL Server Migration Assistant for Access (SSMA for Access) [ Download SSMA 2005 for Access v4.0,  SSMA 20058 Access v4.0,  Access v1.2 ]
  
• Gain access to SQL Server Migration Assistant for Oracle (SSMA for Oracle) (  Download SSMA 2005 for Oracle v4.0, SSMA 2008 for Oracle v4.0,  SSMA 2005 for Oracle V4.0, SMA Oracle v3.1 )
  
• Gain access to SQL Server Migration Assistant for Sybase (SSMA for Sybase) (   Download SSMA 2005 for Sybase v4.0, SSMA 2008 for Sybase v4.0, SSMA 2008 for Sybase PowerBuilder Applications v1.0 , SSMA for Sybase v1.2 )
  

The page says :

If you are ready to migrate to SQL Server from a costly platform such as Oracle, DB2, Informix, and Sybase or if you are ready to move up to a more feature-rich, robust database platform this page provides access to SQL Server migration information that will help you evaluate your decision, and provides access to SQL Server migration tools that will help simplify the process.

We did spent lot of time hunting for the right solution. I hope you find this and save that time to use it productively somewhere else. Good Luck.