The RMark package has been put on CRAN so that you can install it like any other R package. This will prevent any future problems if I add dependencies to other packages like I did with msm, plotrix etc in a previous version. There is only a Windows binary but for Linux you can download the source and build the package. For Windows, it will search the path for mark.exe and if it is found, it will establish the link to it; otherwise, you'll get a warning to set the MarkPath variable for the path specification for the location of mark.exe. For Linux, it does the same thing but for the file "mark" without an extension.
Version 2.0.3 that is currently on CRAN has posed a problem for some users who have posted that the link between it and RMark is broken. I sent a patched version 2.0.4 to the CRAN maintainers and it should start showing up on sites in the next few days. If you want this version for Windows and don't want to wait, send me an email offlist and I'll send it to you.
--jeff