My last client really pulled their collective hairs out about Office and Sharepoint after they kept discovering feature after feature they wanted out of Sharepoint was tied to Office 2003 and they only had Office XP and no budget to upgrade….
Here’s a very useful list that goes over the differences when the client machine has Office 2000, XP, or 2003….
http://www.microsoft.com/office/sharepoint/prodinfo/officeintegration.mspx
Here's just the document: Good_better_best.doc