Hi
the two concepts are maintaining for state of user.those comes under State Management Concepts.
cookies are stored in client system and controlled by server side.
View State are stored and controlled by server side.
cookies are not safe while to store sensitive information.
Viewstate are used for passing data between pages like querystring
and another thing is control level view state is ther.If you don't want to post control data to server when user clicks on form postback button then you can set viewstate of that control is false.
View state are used hidden fields to store control information.
you can see this in real time in web page open view source then you'll see clearly the viewstate information is stored in input hidden control.
This is about Viewstate and cookie.
And here 'm providing some links for better understanding about SMC
http://forums.asp.net/t/983980.aspx/1?Usage+scenarios+for+view+state+session+state+application+state+cookies
And
http://sanelite.wordpress.com/2011/01/12/difference-between-application-session-view-state-cookies-query-string/
I hope I clear your doubt.If not Sorry
All the Best