Moving DB with WP version change & theme change

I am going to be setting up a new theme for someone and upgrading their version of WordPress from 2.9.2 to 3.1.3 at the same time. I’ll be doing the work on a temporary sub-domain at their host so they can view the new theme as I work on it. I’ll need to create a new database for this temporary development site and restore the old database to it.

Since they have an old theme, I’m concerned it might break if I upgrade the WordPress installation on the live site so I don’t want to upgrade it.

So, first question. Can I restore the backed up database from WP 2.9.2 to the temporary site and use it with v3.1.3 or do I need to first install WP 2.9.2 on the temporary development site with the database from 2.9.2 and then upgrade it to WP 3.1.3?

Similarly, do I need to temporarily install the old theme which has its own settings in the WP admin (so I suspect it stores its settings in the DB) or will that database work with the 3.1.3 default theme and/or the new them I’ll be installing and customizing?

Eric