Yes! You can install Puppy Linux even on older machines that use the Legacy BIOS (MBR) system. To do this, you only need to create a single root partition while preparing your disk.
Further, you also need to run the GRUB4DOS program instead of using FrugalPup to generate the boot partition. You can access this utility by pressing right-click on the live desktop and selecting "Setup -> grub4dos."