Are you saying that you can't get your new board work at 100MHz FSB? If so, it's more like a problem with memory timing settings, or the board has deficit caps.
Are you trying to get older version BIOS for the new board? If so, please tell us the revision of your new board and the version of your current BIOS.
Are you trying to get BIOS for the old board? If so, please tell us the revision of your old board.

I guess I added a bunch of useless information. Let me try to explain better:

Instaled CPU is a PII 350MHz 100MHz FSB.
The BIOS version I have in my motherboard only allows for 83 and 100MHz FSB selection.
I know there is a BIOS version that allows also for 66 and 75Mhz selection, and I want it, so I can run the same CPU at 233Mhz.

The motherboard I have is a DFI P2XBL Rev. C
The BIOS version currently working is...er the one in the picture:

The newer revision of the mainboard may no longer have that option in the BIOS because it's not supported any longer. Flashing an older BIOS will most likely brick the board, if it was not made for exactly that revision of the board.

Ok, thanks for the warning. That is not good news though.

I think I may have found a reference to the right BIOS. I remembered having flashed the BIOS in 2000 when I upgraded the hard disk.

RELEASE DATE : FEB. 10 1999
BIOS DATE : FEB. 9 1999
BIOS FILE NAME : PBBZD.BIN
BIOS CHECK_SUM : 02B6266F
UPDATE DETAILS :(1) ADD CPU FSB TO DEFAULT/66.8/75/83.3/100.3/105/110/
: 112/115/120/124/133/140/150 FOR ALL KIND OF CPU IN
: CMOS SETUP.

Now its just a question of finding this BIN file 😀 and pray it is not bugged.

Lotus exe file can be patched to work with faster cpus. Assuming that is the only speed sensitive game you play there is no need for bios, slowdown utilities, etc.

It's a little off-topic, but still useful information regarding BIOS flashes IMO: The Linux tool "flashrom" is 100% your friend. With it, you can wrestle (from my experience) absolutely any board into submission when it comes to flashing the BIOS/UEFI, even if the board is so old or awkward not to have an internal programmer (it understands lots of external programmers). Useful for rescuing bad flashes, too.

Here's a fun story (that none of you asked for 🤣): My "daily driver" PC has a Gigabyte H61M-DS2 rev 1.2 motherboard. In its original form, it's still driven by a BIOS, yet when the stars align just right (e.g. you're booting off of a CD/DVD or HDD with GPT partition table and no MBR) it actually boots UEFI executables. The revision right after 1.2, rev 2.0, switched to a full UEFI with fancy mouse-driven interface. The hardware itself has not changed in the slightest between the two revisions, and so, with forcing flashrom to write the rev 2.0 UEFI to the rev 1.2 BIOS chip, I "upgraded" my board to UEFI for free. Pretty sweet.

Anyway, back to the topic at hand: Filosofia, the file you're looking for is, in fact, here: https://pt.driverscollection.com/?aid=14879 - however, it is meant for rev. D of your board. From my quick googling, there should be no major hardware differences between the two revisions, but the included flasher might still fail. In that case, try flashrom! The BIOS seems socketed, so all is not lost if it indeed goes wrong.

EDIT: I just noticed that site is Portuguese and you're from Portugal, too - coincidence, or did you find the file before me and upload it there? That'd be hilarious.

I kind of lost the nerve about flashing this board after derSammler post, that is why it is always a good idea to share here what one wants to do. That way, even if you think you know everything you need about the subject, other's point of view can lead you to alternative solutions. So thank you all, you all gave very usefull tips/insights. I think I'm going with my countryman's sugestion (How are you C. ? Have a good year by the way.) I don´t have that many BX boards, so I will leave it as is. I'm so excited with my 96 Xmas build and maybe I can play the more sensitive games on that machine. 😀

Hey don't need to be afraid you chicken! eh eh eh