Protected Client Area

Hi,

I have an attorney client who needs his WordPress site (that I'm developing) to provide each of his clients the ability to login and see messages meant only for them and permit each client to upload files pertinent to their legal issue(s) that can only be seen by that specific client and the attorney.

Is there a WPMU plugin that can easily provide this capability?

If not, can you recommend other options?

Thanks.

Neil