permalink for images

Hello
I’m using timthumb for creating thumbnail and the address of images is like :
http://mysite.com/wp-content/plugins/wordpress-popular-posts/scripts/timthumb.php?src=http://s1.mysite.com/2010/10/top29.jpg&h=100&w=100&zc=1
Everything work good but i want to change it to nice looking address like :
http://mysite.com/cache/2010/10/top29.jpg&h=100&w=100&zc=1
or something like that. but every time i try to rewrite new rule in htaccess all of my site broke .
i dont know how can create new rewrite rule together WordPress permalink links.