Yes, you can. There are two ways to do it. In both, you first logon to steam from your dads computer, buy and download the game (through your own steam account of course).
You can copy the steamapps folder as easyrider suggests, but that will grab a lot of games. To just get deus ex:
Method 1:
* Just back up the game from within steam, then copy the backup file to your own computer, and restore from that.
Steam's backup system can be a little unreliable (or it used to be - I haven't used it in a long while). So, if you want a foolproof method, I would also do this:
Method 2:
* Find the "steam\steamapps" folder
* look inside this for a file (not folder) called "deus ex human revolution.gcf" or close to it. Copy that to your hard drive.
* then look instide the "steam\steamapps\common" folder for the "deus ex human revolution" folder, and copy that entire folder to your hard drive.
* Back on your own computer, shut down steam. Then copy this file and folder to the same place in your steam folder structure.
* start up steam, and it should find the game and register it.
I would use both methods. Then try to restore from the backup and if that doesn't work, copy over the files manually as in method 2.
