you can create a swc library of any such classes that you are using in multiple projects. The advantage is that its cached by browser and not downloaded again and again.

Here is the step to create mentioned in the article :
http://askmeflash.com/article/9/optimize-flex-swf-filesize-performance-loading

2) Create SWC file of your common code:- If you are using some common classes that are used in many of your flex projects or different swf files then Create a Library Project of your commonly used classes. Now to add this library to your projects :
GO to Project -> Properties -> Flex Build Path -> Library Path and Add folder containing swc file. Now your selected folder path starts appearing in "Build path Libraries".
Remember to change the "link Type” to “Runtime Shared Library (RSL)". This file once downloaded will be used for all your swf files running on that Computer afterwards.

you cannot share a class in multiple projects. Either create a library, or you can use Local Connection to call another swf(having class inside) and pass it the parameters , get the work done and receive the result. Both swf files should be running if using local connection. But I think you go with the library option that's easy and technically correct.

Fine thanks..
The problem is the class gets updated everytime when the user logs in with new data with respect to that user. so making an swc wont work if the data changes everytime..
am i rite?

You are right. If you want to get the class data, In that case you need to communicate between the two project swf files. If your swf files are on the same page you can use javascript else local connection if in different pages to exchange data.

Yup.. they will b loaded on the same page.. i'll try the JS thing n let u knw if i find a problem. Thanks!!