JJ, one you open up the launcher, do not start the game yet. Instead, look to the very left, right in the middle under the Tekkit2 logo you should see a gear icon. Click it, and once the Tekkit Options window pops up, under the Select Build section, check the 'Manually Select a Build' option. Once you've done that, at the top it should say something along the lines of "1.0.5 - Latest", click it and multiple options will open up, then simply press on 1.0.3, save and exit the window. Now you can launch the game and join the server. Good luck.