We use FreeLDR for the RAM booting, which loads in RAM an ISO (not a HDD image yet).
For the LiveCD for example, the following lines can be added into freeldr.ini:
[Operating Systems]
...
LiveCD_RamDisk="LiveCD in RAM"
...
[LiveCD_RamDisk]
BootType=Windows2003
SystemPath=ramdisk(0)\reactos
Options=/MININT /RDPATH=livecd\livecd.iso /RDEXPORTASCD
FreeLdr will load the "livecd\livecd.iso" file from the boot drive (a USB key for example...) (the switch '/RDEXPORTASCD' explicitely specifies that the file is loaded as an ISO image, with read-only access, etc...).
Then, "ramdisk(0)\reactos" specifies that the kernel etc... will be loaded from the "reactos" directory inside the root directory constituted by the ramdisk, once the ramdisk is loaded.
Regards,
Hermès