the 68 refers to the bottom bracket shell length. the 122 refers to the spindle length. A lot of the newer bottom brackets include spacers to make it fit both 68mm and 73mm shells. This bottom bracket comes in four sizes:
68x115
68x122.5
68x127.5
73x127.5
I am assuming that you have a new crank that is compatible with the Octalink bottom bracket. The octalink bottom bracket will not be compatible with the square taper crank.