I haven't played on a PC in a while, but I'll do my best.
Open up the first computer and put a flash drive in. Look for the files ".username" and ".password" on the C Drive. The folder they are in is ".gccg" although that may be in a subfolder (don't remember). The point is, it is not the same place as the update files and other bat files. It is on the C Drive.
Then, open up that folder on the other computer, move those two files right where you found them, and paste. You should be good to go.
Try copying all of the files except for ".history" and that should export your decks too, if I remember correctly.
@Kralik, feel free to edit/correct anything I messed up.
-wtk