Make categories display in different directories?

I’m trying to use WordPress to control all the different sites within my domain, and I have my sites divided into different folder/directories on there. I have WordPress installed in the main public_html directory to manage my blog, but I want to display stuff from one category, which I made specifically for a separate site, display in another subdirectory. I change the wp-blog-header include to point to the exact file but I still get a bunch of parse errors, and it’s probably because the paths to things have changed now. I don’t want to have to install WordPress again in this directory (I really don’t have that kind of space to waste, and it would defeat the purpose somewhat anyway) so is there any way I can do this? Note that I know a lot about HTML and CSS but next to nothing on PHP, so complicated re-writes and hacks aren’t going to work with me.