Using variables

I am working on a portfolio website that has projects listed under multiple categories. I want to try and set up the sidebar navigation to reflect projects that relate to the category the user was looking at. for example: if a user goes services > web > project 1, I want to set up the sidebar to have all of the web projects listed.

But since project 1 can also be classified as a print piece, if they go services > print > project 1, I would like the sidebar to show all of the print pieces.

I am currently working with a dynamic sidebar to try and work these things out.

My question is, ultimately I would like to pass a variable from lets say the web section to the project 1 post then to the sidebar to tell it which posts to list.

Anyone know if or how its done?