Forum OpenACS Q&A: Re: Solaris Zones vs. Xen vs. Vanilla Debian
Solaris Zones sounds like Linux V-Server or the FreeBSD Jail facility. These are all inherently different than Xen. With Xen you can run multiple different kernels, even entirely different operating systems (as long as they support Xen). The new thing about Xen, is that unlike VMware, it can do this efficiently (like IBM's VM) on commodity processors (unlike IBM's VM).
See also these old threads: 2004-02, 2003-06, 2003-02.
The problem with Debian, currently, is that there is no support for x86-64 (neither AMD nor Intel) in Sarge. So either you run 32 bit x86 Debian, or you use the unofficial (and "unstable") Debian AMD64 port. Neither of which is a particularly good choice for people buying x86-64 servers now...