well... if it's just a crack...
you'll need luck, duct tape, toothpaste, some towels, window cleaner and a lot of luck...
9/10 times your disc is fubard...
and for the rest, if you'll play it, you can damage your cdrom...
so.. you have been warned
now...
1, carefully put your disc together,
2, once properly aligned, put the disc shiny side on a flat surface..
3, tape the label side together - put an equal size of the tape on the whole disc...
and here comes the fun part - try to read it, if it fails continue with this>
1, apply the toothpaste on the shiny side... only a little bit...
2, wipe it off, gently, from inside to outside...
3, let it rest for a coffee break... 5-10 minutes..
4, apply window cleaner...
5, wipe off the stuff clockwise...
6, let it rest overnight...
7, try to read it...
also... pray it reads...
and backup everything asap...
and pray even harder it doesn't explode inside your cd rom...
also.. you will lose some data...