Pass arguments to add node.

Hi,
I'm having a problem developing a product review module.

Basically, i have two node types: products and product_reviews.
Each product can have many product review.

Now, on each product page, i want to add a link "write review" that take to /add/product_review for the user to write a review.

on the add review page, i could add a drop down for the user to choose the product he's reviewing, but it will soon become huge.

What I'm trying to do is to pass the product id to the add product review form.
I can't find a way to do it. I want my URL to look something like /add/product_review/productid

Or any other elegant solution.

Thanks for your help.