math question,y=mx+b,it's been too long for me

[sebs]

I need some help from you guys.

i'm doiing something in flash but you will be able to
help me,let say i have a cartesian plan:

   -,-  |    +,-
        |
   _____|_____
        |
        |
   -,+  |    +,+

let say i have a point at 0,0 and i move my mouse on
the cartesian plan,i would like to move the point from
2 or 3 position,but to have the same angle as the mouse

i think i would need the y=mx+b equation but i'm not sure
and i don't remember how to use it,can some body help,
post it in vbcode i'll translate it after!!

example(*=mouse location;.=point)

            
        |       *
        |
   _____|_.___
        |
        |
        |

        |*  
        |
   _____|._____
        |
        |
        |

        |    
        |
   _____|_____
      . |
        |
   *    |

well,something like thaT!!!

THANX FOR THE HELP!!

[SteveCRM]

b is your y intercept (where your line crosses the X axis)
m is your slope (example: 3 = 3 over 1, so you would go up 3 and over 1)