ACT! typically installs its databases in a dedicated SQL instance with credentials only known to Sage. If you have a support agreement in place and are prepared to sign a disclaimer, Sage "should" let you have those credentials.
Alternatively, use ACT!'s built in scheduler to create backup jobs and backup the resulting files using a "File" backup set. If you can get the "sa" credentials, you may create and use a Microsoft SQL backup set to backup the database.
It may also be helpful to Google: act sa password utility