First url rewrite

This is my first url rewrite and I am struggling. I watched the video by Ruslan Yakushev and made a number of trys but haven't got it to work. I beleive it should be simple.

Sample url

http://www.mydomain.com/Category/main.taf?cat=1&pc=1&gpc=1&crumb=1

needs to be permanately redirected to the following

http://www.mydomain.com/Category/main.taf?cat=1

I am trying to remove that last there arguments. The url doesn't neccessarily have to include all three - pc, gpc or crumb. May be all three, may be one or none. Each of the last three argument could be any number.

The first argument (cat) could be any number as well.

Also looking for a Windows URL Rewrite for Dummies with lots of examples.

Thanks in advance for your help.

Steve