Right thanks for Blue for helping me figure this out, if you want to add extra animations to the stock humanoids from the Unity Asset store the following worked for me:
1) Start a new project in 3d Studio Max
2) Click Animation->Bone Tool
3) From the right hand pane select "Biped", click in the viewport and size accordingly.
4) Animate the biped anyway you like(lots of tutorials on youtube), Note you do not need to add a mesh.
5) Click on the viewport and press Ctrl-A to select everything
6) Click file->export and save the FBX anywhere you like
7) Drag the resulting file into the Assets in unity
8) Click the imported file and in the right pane in unity click Rig then select the animation type as humanoid, click Apply.
9) Click the little play button on the icon for the asset you just imported.
10) You should see something like take 001 - thats your animation
I managed to get this to play with lots of different asset store bipeds and all seem to work fine, please note i'm by no means an expert in either pieces of software but I needed a quick way to add animations to existing characters so I can get on with learning unity rather than 3ds Max etc.
It should be noted also that the standard 3ds Max biped comes with hands but not fingers so thats something extra to figure out but all in all its actually not that hard!