If so then then the Xda geeks have an excellent opensource application called Heimdall that does exactly that!. Unlike many other tools this opensource app run in GNU/Linux, MS Windows and Mac OSX as well.
It has two main version (before you panic, they're both free :P). One version is a command-line tool without any GUI... but the other is a graphical frond-end that uses the command-line tool (written in Qt toolkit I assume).
*. According to the developer they've tested in various Galaxy S variants such as - GT-I9000, GT-I9000, AT & T Captivate, Vibrant Bell, Telstra I9000T-GT, and the Epic 4G Galaxy Tab and in all those occasions Heimdall has done its duty quite well and seems to have a 100% success rate!.
*. Load the ROM file and it'll show various info such as the Version, Platform, and supported devices, etc.
*. Repartition if necessary.
*. Showing the progress.
But please remember. While using it do not remove the USB cables which will result in a ROM flash/update failure resulting in a non-usable Galaxy S device :/. Also make sure you have a power backup generator (UPS devices, etc).
And lastly even though this has a 100% success rate yet there's no guarantee that it'll work 100% for you and both the developer and myself do not hold any responsibilities for damages that could occur in your Galaxy S ROM flashing procedure.
You can get the latest update 1.3 (still in beta) from this Xda forum thread. Oh one more thing, when downloading choose "Heimdall-Frontend" if you want the GUI instead of the command-line tool.
While I was installing Heimdall 1.3 in Ubuntu 11.04 Natty Narwhal I also had to manually install a Qt-4 XML library using the below command. Your Ubuntu installation may have it already but after installing if you couldn't run it then use the below command.
sudo apt-get install libqtxml4-perl
After installing, just press "Alt" + "F2" and put the below command and it should run automatically.
So if you've been wanitng to flash your Galaxy S tablet/smart-phone in Ubuntu, then Heimdall is the one you should be talking to :). I hope this works for you. Good luck.