Where does the Browser save the tracks?

The tracks in the Silverlight version are saved in [Drive letter]:\Documents and Settings\[your user name]\Local Settings\Application Data\Microsoft\Silverlight\is\[random letters]\[more random letters]\1\s\[more random letters]\f\

Play Line rider once on the 2nd pc and save a track (just draw a line since it will be gone anyway). Copy the linerider.xml file and the other files in that folder on the 1st pc to the corresponding folder on the 2nd pc. Click yes to overwrite if asked.

Another option is to copy the entire [Drive letter]:\Documents and Settings\[your user name]\Local Settings\Application Data\Microsoft\Silverlight\ folder to the second pc at that location. However, this will replace all saved silverlight data (from other sites that use silverlight) on the 2nd pc, so be careful if you saved something on another site that uses silverlight on the 2nd computer. However, most sites use Adobe Flash instead, so this will most likely not be a problem.