Thru your network, if you have them network connected together. Or copy onto a USB 3 (or 2) external hard drive, then copy from there onto your other PC. I copy all of the Trainz directory, rather than just the data folders "local" & "original"
I recently had a 5 year old Segate 3TB internal HDD fail completely. Luckily I had the TANE SP3 beta, (550 gigs, approx) backed up on both and external USB 3 drive & my NAS. I brought and installed a new 3Tb internal HDD. It took me less than half a day to copy the backup copies of Tane SP3 beta (& TS2012) onto my new internal HDD.
I backup most of my Trainz installs onto a USB 3 external hard disk drive & my NAS. (It the Irish in me, to be sure, to be sure)... :hehe:
Cheers, Mac.