Handling multiple implementations

[Nishad]

Hi

I would like get an expert advice on
How to manage multiple implementation of
A product (asp pages). One product implementation
is based on our base product, but 5% of 
The total pages may need some customization.
Can somebody suggest how to manage this scenario
Using CVS. 

Is branching for each implementation a good option?
Is there any way that the changes made to 
One of the files, which is common to all 
Implementations be transferred to all the 
Implementations (for eg. bug fixes, etc.)

May be I can explain little further.

I am starting with project with three pages, a, b and C.

Starting a branch ("z_branch")for Client Z.
a and b  are same as the base version and c modified to 
satisfy the client requirement.
Also one extra file 'd' is added to the project.

Started another branch ("y branch") 
A and b are same and c is different - no d

After some time - we found a bug in 'a'. Is it possible to do 
the bug fix in one place and update the two branches with this update.


Thanks in advance,

Nishad