Ruls for same URL

Hi,

I am new to url rewrite. How can I write 2 rules for same url?.

for instance.  I have:

    myproduct.asp?id=1122&category=cars

which I can write a rule with no issue, BUT if I have the same url with extra variables attached to it like:

   myproduct.asp?id=1122&category=car&model=ford

Then how can I write the second rule to use this url to encode it to the browser.

Thanks in advance.