Using ASP:

1. Get the other site to link to yours with a ref ID like:

http://[yourdomain]/[page].asp?ref=4

2. use request.querystring("ref") to get the number

3. use SELECT CASE to decide which logo to show depending on the number sent

4. use request.servervariables("HTTP_REFERER") to get the other webpage they came from

5. place the HTTP_REFERER value in the form as a hidden field