Update Rollup 1 is available for Microsoft Dynamics CRM 3
His team has released Microsoft Dynamics CRM 3.0 Update Rollup 1 for Server and Sales for Outlook. This Update Rollup makes it very easy for customers to update their Microsoft Dynamics CRM 3.0 systems to the latest set of hotfixes, and to maintain parity between the client and server components of Microsoft CRM 3.0.
Microsoft Download Center: http://www.microsoft.com/downloads/details.aspx?FamilyId=08BADB01-4984-458E-96E6-4F08622CFE63&displaylang=en
Microsoft Knowledge Base Article: http://support.microsoft.com/kb/922815
If you are looking for 2007/Vista compabatabilty, look here.
When customizations were exported from a Microsoft CRM 3.0 server running Update Rollup 1, importing the customizations to a Microsoft CRM 3.0 server that does not have Update Rollup 1 installed is not supported. Such an attempt will produce an error message such as “The selected schema file does not conform with the requested format. There has been an error with the schema validation in line 37977, position 16.” When attempting to import customizations to your CRM Server that were exported from a CRM Server running Update Rollup 1, make sure the CRM Server to which you are importing the customizations also has Update Rollup 1 installed.
Update Rollup 1 contains hotfixes and updates that you have to manually enable or configure. To enable or configure these hotfixes on the server that is running Microsoft CRM 3.0, consult the "Hotfixes and updates that you have to manually enable or configure" section of Microsoft Knowledge Base article 922815.