Maybe but given how touchy XML can be, I'd verify. But that's a thought - if you can keep Project 2003, can you use it as a "passthrough" -- have it set up to import/export the .mpp and you can still link to 2003?
The problem, however is that if you use anything that's newer to either 2007 and 2010, it may not be able to export correctly back into 2003 .mpp.