Subject: revalvity of motion

MY mind has recently boggalled over this one :

To say something is moving, it is neccessary to relate it to something else.  
To say the earth is moving at Xkm per hour, we first must take the sun as 
being a stationary point (which of course it is not).  Compared to a near-by 
sun, the earth is moving in a differnt direction and speed.

My question is this : If all movement is only relavent to something else, how 
can we define a stationary object or point of the universe? If all movement 
is relative, how can we define the speed of light?  Or is there some phycical 
way of finding the 0 speed of the universe?

Thanks a lot for your time.

Re: revalvity of motion