that is the question.
HORM (Hibernate Once Resume Many) boots a system from the standrad XP hibernation file. This can be quite fast (under 10 seconds), if the amount of RAM is not too big.
The hibernation file always has the same size as the available RAM and therefore reading in 2GB of RAM e.g from Compact Flash can be slow! Nevertheless, I have seen systems booting in 8 seconds with 2 GB of RAM having a Pentium dual core and a hard disk. So, if processing power and a fast hard disk is available, it is possible to use HORM even with larger amounts of RAM.
Tip: You can use the /maxmem swith in the boot.ini to limit the RAM size to find an optimized setting fitting Your scenario.