How can i pass VBScript variable from server side, ASP, to client side
and and vice versa ?

you need to look into remote scripting

http://msdn.microsoft.com/scripting/remotescripting/default.htm

Although you could look into Remote Scripting, as suggested, if you are
simply wishing to pass a variable from Server to Client and vice versa,
then I can suggest the following techniques:

Server to Client:

In the response, write a piece of client side script, but initialise a
variable with the server value, something like this:

Response.Write "Dim ClientVariable"
Response.Write "ClientVariable = " & ServerVariable

You will then have a variable that you can use at the client side with the
same value.  You might not want you implement it quite like this, and
obviously you'll need to modify it for strings, and it won't work for
objects, but you get the general idea.

Client to Server:

Just use a form, or pass it in the URL as a query parameter.

Hope this helps.

Steve.