to take full advantage of 64bit architecture, I'd advise to install 64bit distro instead of 32bit one
you don't really need to compile kernel from scratch unless you have some specific needs. just add the following to your /etc/apt/sources.list:
deb http://download.openvz.org/debian-systs etch openvz
deb-src http://download.openvz.org/debian-systs etch openvz
and, import the key
wget -q -O - http://download.openvz.org/debian-systs/dso_archiv_signing_key.asc | apt-key add -
and do:
apt-get update && apt-get install ovzkernel-2.6.18-smp
(assuming you use multiprocessor or multicore server)