The key to adding a MySQL instance as a linked server within 64-bit MS SQL Server is finding an appropriate x64 ODBC provider. Microsoft had previously depreciated and eliminated this feature for the 64-bit version of SQL Server.
They recently reversed their decision, and claim no new plans to depreciate this provider. However, the link is slightly hidden. Here it is: http://www.microsoft.com/downloads/details.aspx?FamilyID=000364db-5e8b-44a8-b9be-ca44d18b059b&displaylang=en