Hi,
thanks for you answer. Here the results of the file command - I hope it's that you want. 
# file /boot/vmlinuz-2.6.20-ovz005
/boot/vmlinuz-2.6.20-ovz005: x86 boot sector
# file /boot/vmlinuz-2.6.18-openvz_xen
/boot/vmlinuz-2.6.18-openvz_xen: gzip compressed data, from Unix, max compression
I had big problems with the pre-build kernels during installing my server in April. So I am not using prebuild kernels and using my own one. So i cannot tell you, if it will run. The second problem is, it's a productive server. So i don't want to "play" so much...
Rgds, Tobias