I know Microsoft don’t offer support for Office 2003 anymore (unless you have an extended support agreement), but as we all know there are still lot’s of places out there especially in larger Enterprises using Office 2003 on Windows XP.
Microsoft quote office 2003 as supported by SharePoint 2010, and the document here http://go.microsoft.com/?linkid=9690494 suggests if offers a “Good” level of interopertion with SharePoint 2010.
However here’s a tip for you, based on an issue we encountered during a SharePoint 2010 upgrade from SP1 to DEC 11 CU, I would suggest if you have Office 2003 clients don’t upgrade your SharePoint 2010 instances past SP1 if you have document libraries with multiple content types associated (later versions of Office 2007 / 2010 work fine).
You’ll get this error message ‘this.frm.ctNameToId’ is not an object, when you attempt to save a document for the first time into a library.
I have compared old and new versions of the function where the error is thrown “function ChoiceFValidate()” and can see an extra few lines of code have been added compared to the earlier version, see below
SP1 Dec 2011 CU (BFORM.js)
Why this would cause Office 2003 to break is not clear at present it maybe due to the form configuration we have on our content types on our document libraries??
Either way we see the issue on versions of SharePoint 2010 SP1 DEC 2011 CU, and the file change date time for the BFORM.js file is 16/11/2011.
So if you have Office 2003 & Document Libraries with more than one content type, stick on SP2010 SP1 until you can get your users on a later version of office. Might take this one up with M/Soft to see if they have a suggestion, might also investigate if a later CU from 2012 sorts the issue, hope you don’t have the same problem we did.