CvsIn is not integrated by means of the SCC API or SCC COM interfaces. SCC API interface for CVS (CVSSCC) project can be found at:
http://members.home.net/preston/cvsscc.html

CvsIn is not a stand-alone tool. To use full set of features that CVS provides you need some external utility (Browser). Browser will let you to operate on a per-directory basis and perform many complex operations.

CvsIn is only operating on a per-file basis. It is designed to cooperate with the browser (and to perform simple per-file operations and indication of the file state at the later stage of development). The Browser of choice is WinCvs, latest version recommended. Starting from WinCvs 1.1b12 WinCvs has a GoToFile patch of mine integrated. This particular patch was specifically tuned to serve the cooperation with CvsIn smoothly (as a side effect however it makes possible effective use of WinCvs together with other tools, like file-browser tools - Windows Commander is one of the recommended).