There's a rather long discussion on this topic in the below thread. See if it answers your questions:
The only way to "link" swfs is to have one Catalyst project contain the published swf of another Catalyst project. This is a little complicated, because the run-local swf works only when you load it from your local file system, and deploy-to-web only works when you load it from a server. Best practice is to create a single Catalyst project, and publish to a single swf.
Do you know what is causing your project to be large? Is it particularly large image assets?
If so, Catalyst 1.0 will have some additional options for optimizing images that can dramatically decrease the size of your swf.
well its not so much the images its all the pages the site needs :/. Im at 15.4mb almost. would going down from a 1024x768 resolution be a bad thing?
Here is another thread on keeping the overall file size down:
Additionally, using "Convert To Optimized Graphics" may help:
You should save a copy before trying these optimization strategies (including decreasing the resolution). All three might bring your file size down.