This file reminds me of MSDOS.SYS in Windows 9x, only shorter and sweeter, at least around here.  I made only three changes to the default boot.ini file after Windows XP was installed.  One was to set timeout to 0, the other two were the switches, /fastdetect and /noguiboot.  By the way, boot.ini is in the root directory (usually c:\).  My favorite way to edit boot.ini would go something like this if you did it manually:

Start Menu / Run... / type CMD / press ENTER
attrib +a -s -h -r c:\boot.ini
edit c:\boot.ini
do the edits
exit the editor
type attrib +a +s +h +r c:\boot.ini and press ENTER
exit the command window by typing EXIT and pressing ENTER (unless you have other business there)

To keep it fast and simple, I put most of the above into a batch file that looks like this:

@echo off
attrib +a -s -h -r c:\boot.ini
edit c:\boot.ini
attrib +a +s +h +r c:\boot.ini

<><><><><><><><><><><><><><>
Here's a brief explanation on how to make the lines above into a batch file:
    - Copy the lines (starting at @echo off, ending at attrib +a +s +h +r c:\boot.ini) into the Windows Clipboard, by left-dragging your mouse over the text to highlight it, and using Copy from the Edit menu.  Or highlight the text, right-click it, and choose Copy from the context menu.  Be careful not to copy any empty space before the first line and after the last, else some of the lines could get shunted to the right when you follow the third step.
    - Start Menu / Run... / type notepad / press ENTER
    - Use Edit / Paste (or right-click / paste) to place the text into Notepad.
    - Choose File / Save As... / give the batch file whatever name you want, only make sure it has .bat as an extension, and is surrounded by quotation marks (e.g. "bootini.bat").
    - Pick your location from the Save in: box, Desktop for example.
<><><><><><><><><><><><><><>

<For more on batch files, visit Gord's World of Batch Files and become a member of the free Batch World mailing list.  Still more info on batch files can be found here at Windows Support Center, and here at Computer Hope.>

Here's what boot.ini looks like on this machine:

[boot loader]
timeout=0
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional" /fastdetect /noguiboot

timeout  determines how long (in seconds) the boot menu will show... reminds me of the BootMenuDelay switch in Win9x's MSDOS.SYS
/noguiboot bypasses the boot logo  ... I saw it once, once was enough
/fastdetect tells NTDETECT not to check for parallel and serial ports

Taken together, these three help keep XP from doddling too much at boot time and trying my patience.

There are other ways to edit boot.ini.  MSCONFIG is one way (see System Configuration Utility)
    - Here is another from Microsoft
    - Here's one more, also from Microsoft
    - Boot.INI Options Reference at Sysinternals
    - This one at WinGuides, is called Using BOOT.INI Startup Switches

Had enough of boot.ini?  Of course you haven't!  So here's one more item, Additional information and help with the boot.ini, located at Computer Hope.