How do I make the guest OS think it's using a single core Pentium IV CPU?

[Valso]

I feel like playing some old games which run fine in linux up until the point they decide that a quad core is more than they can handle. These games were made back in the days when the multi core CPUs weren't even an idea. But every time I install a guest OS (Windows), it shows the host's CPU. So, is there any way to make the guest OS think it's using this particular CPU: Intel Pentium 4 Processor 2.66 GHz, 512K Cache, 533 MHz FSB?

[FranceBB]

There's a command line option that lets you set the CPU displayed to the guest, so in your case it would be:

VBoxManage modifyvm "Name_of_your_VM" --cpu-profile "Intel Pentium 4 3.00GHz"

Remember to also set the number of cores in the vCPU to 1 from the GUI in the processor tab.