To fill an orbit with enough shrapnel to make it unusable would take both an orbital launch capacity, and a lot of launches. Doing this to geosynchronous orbits would be even harder.

That being said, a "pop-up" ballistic launch that places a load of shrapnel in the path of something in low earth orbit, say a space station, would be a lot easier from a launch capacity standpoint. It requires only enough launch capacity to fly straight up to the altitude of the target--far less than is required to go into orbit. The shrapnel would be dispersed, probably by an explosive charge, in the path of the target just as it approached that location. The latter would hit the shrapnel cloud at orbital velocity.

Obviously, since the shrapnel cloud would immediately fall back to earth after dispersal, some pretty close timing would be required. The orbit of the space station is public knowledge. I believe that it's the delicate timing and guidance issues involved in this attack that make it, hopefully, too difficult for most aggressors.