Really depends on the bottom bracket you have. If it’s a sealed unit, it’s garbage and just replace it with the same size. There are 2 dimensions if I recall; one is the size (width) of the unit itself and the other is how far out the axle comes out, which in turn determines how far out the crank arms will be. I believe the Sheldon Brown site is a good place to start on this.
http://sheldonbrown.com/bbsize.html
For the fork, if you don’t need to replace the headset, it’s as simple as the carb. Just remove the top cap completely first, then loosen the bolts holding the stem onto the steerer. Stem pops off, fork will drop out through the head tube. Be careful to note how the headset items come out, so you can assemble the same way after. The parts just sit on top of each other and are held firm with the stem and top cap when all is tight. Final advice is to replace the fork with one who’s steerer tube is the same length or longer. If longer, make sure you have some spacers handy, as most of us frown on cutting down the steerer tubes anymore since they don’t make retro forks anymore, and cutting will only ensure compatibility with same size bike or smaller.
Good luck!
