Outlook 2003 and Outlook 2007 allow you to export your contacts to CSV format. Is there a difference between the two or is this in fact the same format; in other words, are they backward compatible or did Outlook 2007 create some new fields that Outlook 2003 would have trouble importing?
Well, CSV stands for comma separated values. In both cases, it will be a bunch of text fields, with commas between each. So in that sense, it is the same format.
I don't know if the same fields are exported from each, and I don't use or have access to either.
On my test-machines with Outlook 2003 and 2007 exporting with the default fields gives me identical files. Exporting in 2007 and importing that in 2003 also works fine.
However, MS doesn't document anywhere what that order is and you thus can't take it for granted.
Outlook itself should deal fine with differening order and missing entries as all the properties are named in the first line.
Without guarantees, if you are working in an corporate enviroment where you can test it there are no hard issues.
Otherwise you should do extended testing or try to get a statement from microsofts support.
When you export and import files, I think Outlook remembers any changes you might make using the "Map Custom Fields" advanced dialog. So if you have never been into this, you'll probably get the same result every time in 2003 and 2007.
But if you've ever been into this dialog in either 2003 or 2007, and changed something, you may start seeing different results.