[Galaxy S I9000 Q&A, Help & Troubleshooting] froysm:
Don't worry, that is exactly why we are here to learn from other people experience and share what we have learned.

About your issues,

I only have access to my Linux machine and heimdall says this when i ask for help (with the command

heimdall help

Usage: heimdall <action> <arguments> [--verbose] [--delay <ms>]

action: flash

arguments:

--repartition --pit <filename> --factoryfs <filename>

--cache <filename> --dbdata <filename> --primary-boot <filename>

--secondary-boot <filename> --param <filename> --kernel <filename>

--modem <filename>

So, what you have to do is navigate to the location of your files and write something like this

heimdall flash --repartition --pit s1_odin_20100512.pit --factoryfs factoryfs.rfs --dbdata dbdata.rfs --cache cache.rfs --param param.lfs --kernel zImage --primary-boot boot.bin --secondary-boot Sbl.bin --modem modem.bin

See how i reordered the files to flash leaving at the very end Sbl.bin and modem.bin?

As i told you before this will fail because of the last files, but it will allow to flash everything else. Remove your battery, put it again and try to boot your phone.

I forgot to tell you something really important!! Since the flash in going to fail it will give you the <<scary>> "Connect phone to PC" screen, but don't worry, heimdall can take care of that. Again, asking heimdall for help in the command line says something like this:

action: close-pc-screen

description: Attempts to get rid off the "connect phone to PC" screen.

And that is exactly the next step to take, write down in your command line (with the pone connected to the pc and in download mode)

heimdall close-pc-screen

And that's it, wait for the phone to boot.

This method is the one i advise when you just can enter Download Mode or when you really need to repartition.

Better? Worse? Nah, they are just really different approaches, Odin is the Samsung standard, Heimdall came to the game because it's OS X and Linux compatibility and CWM allows you to control your phone, custom kernel settings, flash updates packages with modems, boot animations , even whole roms without the need of a cable to connect your phone to a PC and other really cool stuff. Generally, since i've been in custom roms (like darky's, romkitchen, ultimate, etc) since i got this phone, i only use CWM, and when i have a big problem or i need a stock rom i use Heimdall (because i'm on Linux).

The CWM version is just fine, not all the roms are compatible with CWM 3 at the moment, so just make sure you can mount your phone in your pc with CWM. Try first the CWM option, if you can't mount it or it just don't works try the heimdall option.

The last question, I'm not saying it's 100% safe because it is not, but not only custom roms, this also can happen flashing a rom with Odin or Heimdall. Honestly i haven't heard of someone who bricked a phone in the whole thread of the romkitchen or darky's rom. I mean, it could happen, even with a perfectly stable stock rom. but it's not so common, at most, the worst thing you will encounter in your custom rom experience is a lot of Force Closes in applications (if you mix data and apps from incompatible versions) maybe a couple of boot loops, but nothing to be really scared about, just make sure you can enter Download Mode and everything will be fine.

Phew! The longest post if ever written in any forum. I hope i made everything clear, if you happen to have any other question i'll be happy to answer it (But it will have to wait for tomorrow... you know, it's midnight).