Ok, for access I suggest
http://www.thinkgeek.com/gadgets/security/c49f/
Now the question is the OS of the box. I cant help much with MAC, but if its windows...
As for putting up porn... ehh.. just start with an innocuous windows system file like system 32... then select a random file, open it, make a file with a harmless sounding name like Host, open that file, make a file inside of it, wash rinse repeat about 10 files deep, then in the last file dump your traceable pr0nz. It will be hidden well enough without anyone noticing its there, but in the case of forensics and someone looking for it, they WILL find it. But you can also go to the properties of the file, and convert it into a hidden file. Again 90% of people wouldnt find it because they arent looking, but someone who is purposely looking for it and has a degree of understanding on how to find things, would likely find it.
If its a program of sorts you can follow the same technique. make a deep directory of files. During program installation, redirect the install path to that deep file, and select to leave no start menu/desktop short cuts. Only thing to be concerned with is that anything installed will still show typically in the add/remove programs file registry.
If thats your intent what you can also do is install the program to get it to show in that list... then go back to the file where you installed the program then delete the file. It will still show up in add/remove program registry but there is no trace of the files to be found anywhere. (basically doesnt uninstall just deletes the primary files, registry markers are still present)
You can password protect files that have been compressed such as Winrar files, to keep people from opening them, but problem there is that they are still compressed and basically unusable in a program standpoint. (perhaps archived as an ISO that has to be mounted and P/W protected?
Now, if your wanting to install a game to use on someones computer and basically leave no trace? Install the game to a flash drive big enough to hold that installation. Insert the flash drive to the PC you want to use it on, and run it from the flash drive. will not leave an imprint, and will in most cases run the same as if it were installed on an internal drive (though there may be some extra load time from dealing with slower flash memory)