How to flash Samsung devices from a GNU/Linux host running on ARM architecture? To flash a Samsung Galaxy S (where do not have root access in the currently running OS, and with a stock recovery) with a new firmware (OS), I need to connect it with a USB cable to another computer and flash it from there.

There is a further problem if the other computer (which runs a GNU/Linux, Ubuntu) is ARM (it's a Toshiba AC100). So to flash a new OS onto the Samsung Galaxy S through the USB cable from the other computer, I'd need something like heimdall for ARM. It's not among the available pre-built downloads for heimdall. Perhaps, I will have to try to build it for ARM then... 

Is obtaining heimdall for Linux on ARM possible?
ARM is currently not supported officially by heimdall.
You might have luck compiling it yourself:  

https://github.com/Benjamin-Dobell/Heimdall/

My advice however:
Use a supported platform once (Win/Mac/Linux-x86/x64) and enjoy on-device updates from then on via ClockWorkMod recovery (CWM) or RomManager.

Reason: Heimdall is only needed to install a bootstrap CWM once. After that you use the regular CWM.

Here's the guide from cyanogenmod:
http://wiki.cyanogenmod.com/wiki/Samsung_Galaxy_S:_Full_Update_Guide

CyanogenMod releases for CM7/9/10 in various flavours (stable, release candidate, nightly build) can be found here (Galaxy S i9000):

http://get.cm/?device=galaxysmtd