I take it you're using a Mac then? I'm not to familiar with Macs or Heimdall. 2.3.4 onwards uses 512.pit
file, make sure you have "re-partition" checked. The firmware .zip files usually come with the .pit file
It's up to you what firmware you decide to use. The most current one available for flashing is 2.3.5 JVT available at samfirmware.com. This page http://www.samsunggalaxysforum.com/samsung-galaxy-s-updates/%28official%29%28firmwares%29galaxy-s-i9000-download-only/
has all the firmwares available. Ignore the part that says:- First check your firmware *#1234#
- Check Simlock and Network lock is OFF *#7465625#
- Make a hard reset after your flash code: *2767*3855# (for safety)
These are secret codes and I've had trouble with them before so I advise not using them. You can hard reset in Clock Work Mode (CWM) which you access by switching the phone off, press and hold (in this order
) VOL UP, MENU & PWR ON. A small menu comes up and you can select wipe there.
It's also a good idea to back everything up first, wiping before flashing and wiping after flashing.