Yes it is relatively easy. My car is a 2001 325i with manual trans. The only real trick is to replace everything (radiator, expansion tank and 4 hoses=about $430). At first I did not replace the expansion because it wasn't leaking but it did leak when I put the new radiator in, so I had to drain the lines etc. when it would have been much easier to do the job only once.
The hoses will be VERY stuck but come off with a little tapping, or some light pounding and prying where necessary.
Basically here's a summary: Remove the air filter housing and the tray under the car. Drain the radiator and remove the hoses. Then the electric fan comes off BEFORE the expansion tank comes off. One bolt and 2 clips on the fan I think, and the electrical connection, and it just sits in some clips that cradle it at the bottom of the radiator. Then, the expansion tank has one bolt on the left top (I think) and one bolt underneath, AND the tricky part, it has a hidden peg on the lower left, so after you remove the obvious bolts you rotate it AND the flat plastic thing it mounts on (the axis for the rotation is up-down) toward the rear and to the left to slide the peg out of the hole. The radiator itself is easy. Just pay attention to the clips. You can pull it up of drop it down, whatever you like.
The "4th hose" goes all the way to the back of the engine but if you remove the microfilter housing it is easy to get to, although it won't look like it at first.
Use BMW antifreeze. You need the star-shaped allen-keys, so get a full set.