[ubuntu] Which virtualbox or qemu

I've tried both virtualbox and qemu on my machine, but neither of them seems to work.

My machine is HP pavilion a6622sc (Phenom 8550) running 32-bit Ubuntu 14.04 LTS.

Which is the defining thing: 32-bit Ubuntu or 64-bit HW?

Also, any pointers to tutorials about debugging a small RTOS using those (virtualbox, qemu)?
(How to get the debugger working.)
The RTOS is for x86 only.