In TRS2006 the "Local" file has all your assets and routes.
I regularly copy my "Local" file to an external hard drive, just in case I need to transplant the file into a re-install of TRS2006. (My "local" file is 780Gb and takes like an hour to copy over all the files, don't sit and watch it, go shovel snow or something ... if in Australia, go take a swim at the 80F beach).
Send your original "Local" file to some where (a flash drive memory stick, DVD-RW, External Hard drive, or your Desktop ... etc ... etc
If you are instaling on a second PC, or re-installing TRS2006 its factory fresh "Local" file will be deleted (or moved somewhere for safekeeping) ... and the New Local file will be drag and dropped into the TRS2006 folder.
The files: assets.tdx & assets.bku -(in casche) should be deleted.
Restart your PC ... Restart Trainz and the TAD will rebuild, and your New Local file with all your assets and routes will be in the re-intallation.
Hopefully this still works ... as my TRS2006 is no longer updating its DLS, probably because of server problems , or the unsupport of 04/06.
NOTE: None of these techniques are used in transfering TRS2006 files into the TS 2009 or TS 2010 versions ... as it will corrupt 09/10