ROM parts description (usually you’ll get the ROM as compressed files; I suggest you to extract the actual rom files using 7zip becouse it is compatible with every form of compressing out there and it’s freeware too; if the files looks something like zip.001, zip.002, etc or part01.rar, part02.rar, etc just extract the first file and it will automatically extract all the needed parts)

Eboot (.eb0): some users compared it to a PC bios; another user posted this definition “it’s a part of I8000 software that provides the very flashing process. In other words it’s a program that replaces PDA, CSC and phone parts of existing firmware to updated ones in I8000 read-only memory”
Sorg affirmed that the only risk of bricking your phone comes from “eboot”: if Eboot will be corrupted during replacement to newer one then you will likely lose the option to save your i8000. That is why changing Eboot is not recommended on every-time basis.
Personally I’d suggest to flash eboot only while upgrading from WM6.1 to WM6.5 (that’s the only time I flashed the eboot), becouse it seems that not flashing eboot may cause a problem about your phone not going into sleep mode. I had the problem too and solved it by flashing eboot. I guess this was needed for going from a old wm6.1 rom to a new wm6.5 rom, so maybe it will not be necessary again in the future.
So in the end, even if I still suggest to not flash eboot when is not needed, if you are facing some weird problems it may be worth to flash it too.

PDA (.mst or .nb0): the actual Windows Mobile OS, applications, drivers, etc

CSC (.csc): definition by Rodfigofd “Among other things, it contains boot images (not the animated ones, that correspond to power_on/off.gif, but the one that goes before that), much like the HTC devices’ splash .nb files, .. also, the charging animation when device is plugged but off, animations for the EBOOT program when you are flashing the phone, and also files and settings that get applied to your Win Mobile when you flash or hard reset. CSC can include, for example, wallpapers, themes, connection settings, etc. I suppose it can also contain apps an other stuff.
Although in flasher program CSC file seems to let you select languages, CSC file just have possible language choices, but not the files/settings corresponding to those languages. Those are all packed in the PDA part (NB0 or MST).”

Phone (.bin): the radio/GPS firmware
Sorg suggests not to flash the phone part as it may cause problems of compatibility in case of downgrading the rom or if your phone is locked to some operator. He also stated that there is no benefit in it, while other users reports different performance in the GPS fix, etc… honestly I have no idea on the subject, but so far no user reported any actual problems for flashing the Phone part.

SAFE FLASHING
Reading the above you’ll understand that if you want to be 100% safe, you should flash ONLY “pda” and/or “csc”. In case of any error during the flashing, even if you get a non responsive phone stuck on the PC-Phone connection screen, you’ll be able to flash the ROM again.
For this reason, Sorg created the modded Octans Mini which allows to flash just PDA and CSC part. If you want to be safe or if it’s your first flashing attempt, I suggest you to use it.

Software required for flashing i8000 ROM
Windos XP with SP3 (if you want to use Window Vista, read here; if you want to use Windows 7 x32, read here; if you want to use Windows 7 x64, read here)
Samsung_CDMA_modem_4_1_.34.zip
OCTANS Downloader (you can use the standard Attached File OCTANS_Downloader_v2.14.exe ( 920K ) 

Flashing Procedure
The following steps are as suggested by Sorg, there are other procedures which may differ a little (such as not turning the phone off) that still works but this one I’ve been using and tested myself and always fine:
0) Make sure to install (or to have installed already) the Samsung_CDMA_modem_4_1_.34.zip driver.
1) Make sure your phone is not connected to your PC; if it is, disconnect it.
2) Make sure to Turn off your phone.
3) Start OCTANS and fill required fields/checkboxes (MORE DETAILS BELOW on How to use Octans Downloader)
4) Press “Detect” button.
5) Connect Phone to computer (make sure phone was turned off before connecting) IMPORTANT: don’t connect trough USB hub.
6) As OCTANS detect phone, press the “Start” button.
7) Wait till whole operation end; the phone will restart itself once or twice to update everything then its ready to set up again.

How to use Octans Downloader (details on the above point 3 of the Flashing Procedure)

– if you use Octans 2.14, you are able to flash any of the four ROM parts
1) Select the Eboot button and open the .eb0 file
2) Select the MoviNAND button and open the .MST file (if the ROM you want to flash is in .mst format) OR Select the PDA buttons and open the .nb0 file (if the ROM you want to flash is in .nb0 format); choose .mst OR .nb0! not both!
3) Select the MultiCSC button and open the .CSC file; in the drop down box below you can select a region for your ROM (more details on CSC decoding is posted below); in the drop down box above you can select the language.
4) Select the Phone button and open the .bin file

– if you use Octans Mini 2.11, you can only flash PDA and CSC part (also the option to preserve the “My Storage” is enabled by defult)
1) Select the MoviNAND button and open the .MST file (if the ROM you want to flash is in .mst format) OR Select the PDA buttons and open the .nb0 file (if the ROM you want to flash is in .nb0 format); choose .mst OR .nb0! not both!
2) Select the MultiCSC button and open the .CSC file; in the drop down box below you can select a region for your ROM (more details on CSC decoding is posted below); in the drop down box above you can select the language.
IMPORTANT: Octans Mini 2.11 doesn’t support flashing CSC parts for the newest ROMs (not sure since when… maybe after the JAx)