you can encode data for use in a querystring like this:

Dim qs As String =
"this is a querystring"
        Dim encodedQs As String = HttpUtility.UrlEncode(qs)

Its important to be aware though that urlencoding your data does not in any way prevent that data from being tampered with / changed by the user.

if you need to use the querystring and want to make sure the data is not tampered with, you might consider the technique in this article: http://aspnet.4guysfromrolla.com/articles/083105-1.aspx

http://www.4guysfromrolla.com/webtech/012000-1.shtml

The process of encrypting the data will also render the data illegible for your users - effectively hiding its value