Import from 2.6.1

I have a client who I am developing a new website for. They have an old WP installation (2.6.1) that I am trying to export the posts from to the new install.

It appears that not everything is being carried across (for example the file only pulls across 12 posts, yet there are 56 on the original install). Is there a way to make sure the xml file works with the newer version to get all the info across?

Please bare in mind i’m a bit of a novice, and I currently don’t have the option of updating the current WP install as there is no fallback option should things go wrong.

Cheers!