In my opinion, you have already answered your question.
You only have access to Project 2007, that is what you work with, so that is the logical certification to go for. There's no point in getting "certified" in a version that you haven't even accessed, let alone used to manage projects.
There are differences between the two versions, so even if you know 2007 inside and out, you will not be able to pass the 2010 exam easily. Added to that, just because another version is out doesn't mean that every company will be rushing out to upgrade
- there are costs involved, including but not limited to: software licensing costs, training costs, etc... In fact there are still companies out there that are still using Project 2003 and earlier.
Project 2007 will be around for a go while yet :)
-Ken
-Ken | http://ken.wagnerfamily.co.uk
