Create partition on your flash drive (using fdisk or cfdisk). Mark one of partitions bootable in fdisk/cdisk. Format that partition with FAT/FAT32 filesystem: mkfs.vfat -F 32 /dev/sdXY where sdXY is your partition. Mount it and copy contents of PLD RescueCD like x86 and x86_64 ISO image to that partition, to /rcd subdirectory. Make MBR record: ...