[R] Ploting two datasets

[Anderson de Rezende Rocha]

Dears, 

I need your help. I have two sets A and B each one containing 
n lines and being composed by the atributes x and y. 

Three questions:
1) How can I plot A and B both on the same graphic? I need to show 
   that the classes A and B are separable. In this way, I need 
   to plot the points of A as "*", and the points of B as "+", for   
   example. This would result two clouds. 

2) How can I plot the result of question one using multi-levels, that 
   is, a set of ellipsis that start on the mean of A and on the 
   mean of B? 

3) How can I trace an hiperplane separating the classes A and B just 
   depicted in question 1?

I appreciate any help. Thanks for all.