ubuntu server in virtualbox

[Paul Cartwright]

I am running a Debian Lenny desktop, and I wanted to put a ubuntu server in 
virtualbox. When I installed it and rebooted I got this message:

this kernel requires the following features not present on the CPU:
pae
unable to boot - please use a kernel appropriate for your cpu.

what did I do wrong and how do I fix it??
-- 
Paul Cartwright
Registered Linux user # 367800
Registered Ubuntu User #12459