You have to zip the two files before sending them to your mem card. The first folder in each zip should be UDATA. Inside each UDATA file, there is another file with loads of numbers. You need to copy a datelinfo.xbx file from a downloaded savegame, into this numbered folder in each zip, so action replay can recognise the save properly.
If you've already done that, then make sure the two saves (splinter cell profile and the linux_installer) are copied to your xbox HD, and that it's the only splintercell profile on your xbox. Also make sure you are using the original splintercell disc, and that it is not the platinum edition.