How hard is it to move the hard drive from one system to another system, when the 2 systems are different architectures? For instance, I have a PII/333HMz with 128MB RAM that I've installed FC5 on. I want to be able to move the hard drive to another computer, P4/1.2GHz with 1G RAM, different video, sound, etc. I don't want to reinstall the whole OS, and am hoping it's as simple as starting up single user and running a HAL updater or something?

In theory it works, but would be better if you re-install the whole thing. You may or may not run into difficulties depending on the installation and the hardware.

For eg., I had P4 2.8 with 1GB RAM before my current hardware and had FC5 along with it. When i reconnected with this new hardware, it failed to boot, giving some errors i don't even remember(sorry), but after doing some research on the net, here and there, i figured out the problem and had to just pass some parameters to the kernel while booting coz of my motherboard. In any case, FC6 came by and I'm on it now.

My advice:
1) MOST IMP STEP : Backup your DATA.
2) Connect it to new hardware and see if it boots.
3) If booting is ok, check the work environment for stability.
4) If all works well, you're on your way, else re-install.

it should work since there both x86
but like shrikant.odugoudar said it would probably be better to re-install

there maybe some additional complexities such as the bios not being able to boot it

it shouldnt hurt to attempt so i would say go ahead

Unfortunately my situation is such that I don't know if I have a choice. I have a iptables firewall server, and a mailman server. I can't afford to bring them down for long, due to their obvious importance. However, I also do not have access to identical hardware for either of these machines in order to make a test/installation bed. So ... I'm trying to do the best with what I've got.

ooo...well with that i leave you with a "good luck"

The easiest thing I've found to do on such things is to set up the new machine completely with all the services you need to run and test them. Then shut down your old machine and put the new one in its place. If something goes wrong you can quickly switch back to the old machine.

you will find the solution @

http://www.novell.com/coolsolutions/tip/19572.html

My 2c (or 2d):
I have done this (moved a hdd from one mobo to another) in the past, and everything worked fine, but you may need to reinstall your video if you are using NVIDIA oR ATI drivers,
Sound and network card drivers might be an issue too. Not a big problem, we hope.

One way to ease the transition would be to clone your current hdd with dd (see the many threads about this subject on this board).

Then install the cloned disk on your new mobo and boot that. See what, if anything, needs fixing. Meanwhile, you can leave your current system running while you fix up the new one to your liking.