really easy, as hcir said pretty much. The bearing in the hub (sprocket carrier) is different to the two in the wheel tho, its not sealed. Should be able to get them no problem from any decent bearing suppier too and are about 3/4 quid each.
The sproket carrier bearing should knock through no problem at all, I think you can only see the inner part on removal but since your knocking it out it wont matter. The wheel bearings are a little more akward because there is an ally spacer between the two bearings, just use a long drift to get in the gap and once one bearing starts to move from home the spacer will move alot easier and allow you better access to remove the bearings. Just remember to put it back when you put new bearings in! And as hcir said, use a socket thats the same size to knock them home, dont use a socket on the inner part of the bearing just the outer.
All in all an easy job and probably only a few hours to do
