AutoCAD looks for ATC files in the \Support folder under the \Documents and Settings path in the current user's roamable profile. You can obtain the root path from AutoCAD by using a host application services function, as follows:
acdbHostApplicationServices()->getRoamableRootFolder(pCatalogPath);
This function returns a string representing the path to the user's AutoCAD application data. For example, the typical path template is c:\Documents and Settings\<username>\Application Data\Autodesk\AutoCAD <versionName>\R<major_AutoCAD_version>.<minor_AutoCAD_version>\<language-id>. You must append the \Support folder name to this string to form the root path.
When your application initially saves its default catalogs, it must specify this location. Registered tool files appear in a \RegisteredTools folder under this root. Catalog definition files are stored in a \ToolPalette folder under this root. The default location for palette content definition files is the <root>\ToolPalette\Palettes folder.
To resolve tool palette content definitions, AutoCAD looks for palette definition ATC files in the locations specified in the catalog files. These locations are URLs, which means that your tool palette content definition files may be stored either locally, on a network, or on the Internet.