Assuming you read this
http://svn.modxcms.com/docs/display/MODx097/Development+and+Testing+Notes did you follow this:
* Checkout or export the latest 0.9.7 code from SVN at the URL
http://svn.modxcms.com/svn/tattoo/tattoo/branches/0.9.7
* If this is the first time you are building from SVN, copy the file build.config.sample.php to build.config.php and edit the properties to point at a valid database with proper credentials. NOTE that this database does not have to contain anything; the build script just needs to be able to make a connection to a MySQL database.
* From the command line, change your working directory to _build/ and execute the command "php transport.core.php". This process will take an extended period of time (100 to 250 seconds likely), so be patient. (Note: on Mac Mini (1.66Ghz Intel Core Duo with 2GB RAM) running the Leopard development environment as outlined below, this only takes 5-10 seconds.)
* Once that script is finished executing, confirm that you now have a file named core/packages/core.transport.zip and a directory core/packages/core/ containing a manifest.php and many other files/directories.
* Now you are ready to execute the new setup script at the setup/ URL (e.g. http://localhost/modx097/setup/ if installed in a subdirectory of the web root named modx097/).
* Make sure you check both the "Core package has been manually unpacked" and "Files are already in-place" options when installing from SVN.
* If you change any paths on the Context Paths setup step, make sure and move the corresponding directories as appropriate; this is intended for installs from the core package with files not already in-place, where the installer will place the files in the specified locations (assuming the locations allow the PHP process to write to them).