install ubcd to usb disk

1. Mount ubcd503.iso to /mnt

-> sudo mount -o loop ubcd503.iso /mnt

(Read /mnt/ubcd/tools/linux/ubcd2usb/readme.txt)

2. Create mbr:
-> cd /mnt/ubcd/tools/linux/ubcd2usb
-> sudo dd if=mbr.bin of=/dev/sdX

(replacing X with your USB key drive letter)

3. Format your usb disk to fat32

-> sudo mkfs.vfat -F 32 /dev/sdX1

4. Mount your usb disk and copy all files of the extracted UBCD iso to your USB thumb drive

-> sudo mount /dev/sdX1 /usbmnt

-> sudo cp -rf /mnt/* /usbmnt

5. Install bootloader syslinux:
-> cd /mnt/ubcd/tools/linux/ubcd2usb
-> sudo ./syslinux -s -d /boot/syslinux /dev/sdX1

(install syslinux to a directory relative to /boot/syslinux on the device)

6. make the partition bootable:

-> sudo parted /dev/sdX set 1 boot on

Ref:

http://www.ultimatebootcd.com/download.html

ubcd-extracted/ubcd/tools/linux/ubcd2usb/readme.txt