Trying to edit amazon link to only search clothing

Hi there i am just starting out with amazon affiliate marketing and i am stuck on creating a search link.

I am using a search plugin for wordpress but i only want the search engine to look in mens clothing so how do i edit the following link to only search in the mens clothing catergory.

http://www.amazon.co.uk/s/ref=nb_ss_w_h_?url=search-alias%3Daps&field-keywords=$keyword&x=0&y=0

Hope somebody can help me out.

 

have a read of
http://affiliate-blog.amazon.com/2007/04/associate_tip_r.html