What functions can be used for the following

Hi,

I am working with census data and I am trying to create a neat representation of the frequency of a certain demographic in some
city zip codes.

The census has available the number of people living in a certain census tracts, with no option of looking up the demographic by
zip code. What can I do in order to create something like a density map of the demographic by zip code, if the numbers are only
available for census tracts? Would it be possible to download the shapefiles of the census tracts as well as zip codes and then
have Arc-GIS find which census tracts overlap which zip codes? Is there a function that can do that?

Also, I've noticed that creating a heat/density map with multiple point data is not the same as trying to represent density when
only a number is given that is associated with a certain geography.

If someone can talk a bit about this, I'd appreciate it.
Thank you