Sharing PHP Sessions

OK, here's my dillemma.

Because of excessive load on my webserver, I brought a newer one into production and have split HTTP load across them.  Both are using Lighttpd 1.4.something with PHP 5 in fast-cgi configuration.  I now have a problem sharing sessions between the two servers.

I have tried memcached and NFS, and neither are working.  Our wiki is saying it is losing session data, thus failing the commit of a new page revision. 

How the fuck do I fix this?

Don't share sessions, just confine individual users to one server for the duration of their session.

And how the dick would I go about that?

Depends how the load balancing is set up, obviously.