The main website's [url=http://www.linuxmint.com/rel_debian.php]LMDE known issues page[/url] (the one the Welcome Screen links to) says this:
[url=http://forums.linuxmint.com/viewtopic.php?f=189&t=126434#p690427]A forum post[/url] says how to do it:Multi-core and multi-CPU support in 32-bit kernel
To guarantee compatibility with non-PAE processors, the 32-bit versions of Linux Mint Debian come with a 486 kernel by default. This kernel does not support SMP, and as a consequence is only able to detect one core and one CPU. If your CPU has multiple cores, or if you have more than one CPU, simply install the 686-PAE kernel and reboot your computer.
Code: Select all
sudo aptitude install linux-image-686 linux-headers-686-pae