How To Add Specific User Link To End Of URL

I need to be able to add a user's code to the end of the url of each page they go to. I am a user, go to my site and type in my user code - which is NOT a login. There is no password, in theory there will be a box or some type of control that will allow a user to enter their code in. This control will then add that user's code to the end of each URL for every page in the site and will also auto-populate all of the products in our database that are tied to that code. The user is like a business or affiliate marketer. We need that code at the end of each URL that way when he sends his clients emails with links in them for purchasing, the client will click the link, and that marketer will get credit for the sale(s).

I was told to use this code:
<ul id="p7menubar">
<li><a href="<% =GetIB("[URL]") %>">Home</a></li>
<li><a href="#" class="trigger">Lookup</a><ul>
<li><a href="<% =GetIB("Default.aspx") %>">Product</a></li>
<li><a href="<% =GetIB("/FeatureSearch.aspx") %>">Feature</a></li>
[Code] .....

I am now using this code and it seems to be taking it whatever value I type into my textbox:
Protected Sub IBTextBoxButton_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles IBTextBoxButton.Click
Session("IB") = IBTextBox.Text
Dim IB As Integer = Session("IB")
Response.Redirect("IBDefault.aspx?Baccount=" + Session("IB"))
End Sub

<a target="_blank" href="<%# eval("Data") %>?IB=(Session("IB"))"><%#Eval("Title")%></a>
The "IB" gets underlined and says it must be followed by an equal (=) sign and a value. Or if in quotation marks, they must match.