IIS Rewrite or Mod_Rewrite

Hi, I have created a website which is using the iis rewrite module to write the following: index.php?tn_id=5&ln_id=4 to something like /contact/directions.html and this works fine however I have a link at the bottom which needs to pass another variable through the query string before it would simply be: index.php?tn_id=5&ln_id=4&ts=75 however if i run /contact/directions.html?ts=75 it doesn't work and comes up with a 404 page not found error. Is there anyway around this? Thanks Kevin