You should download and install Multiterm coming with Studio 2009, it will work with Trados 2007. Two versions of Multiterm will not work at the same computer.
In case you have the new MT installed but it does not work properly with the old Trados, uninstall MT and reinstall it once more: something might be wrong with the existing installation.
I have only one version (2009) installed. Does Multiterm connect to Trados automatically?
[Edited at 2012-08-28 11:49 GMT]