Thanks for your answer Falko...
I successfully build a load balanced + high availability server (currently in production) on 2 real servers running Xen (instead of having 4 servers...) with http, mysql, mail and dns based on many of your howtos...
Im almost done writing an howto about it, will post it on howtoforge when it will be completed but you can take a peak :
http://blogama.org/?q=node/21
Marc