Recommended user architecture?

[Bernd Fuhrmann]

Hi!

I'm trying to host some private CVS managed projects on a Linux host. 
There are so far three projects in /var/lib/cvs as modules:

projecta, projectb and projectc. There are also some users: usera, userb 
and userc. Now I'd like to restrict access so that:
usera can read projecta and projectc but not projectb
usera can write to projectc
userb can read projecta and projectb but not projectc
userb can write to projectb
userc can read and write everything

So my question is: What would you recommend to achieve this as easy but 
extendable as possible? Would it become neccessary to add all kinds of 
new user groups? Or would it help to create a new repository for each 
project?

Is ssh the right choice for things like that at all? Or would pserver be 
better?

Thanks in advance
Bernd Fuhrmann