Generally, opening an mdb database in Access 2007 is not an issue. I work with that format all the time.
It is likely that your macros aren't running -- security settings in 2007 mean that many macro steps are disabled in 2007, unless you have put the database ni a trusted location. See if this sheds some light...
Also, check out http://www.allenbrowne.com -- there is a good section on 2007 differences and issues.