An annoying update:
I picked up my old and faithful P3 1Ghz running on a decrepit Matsonic MS7157C (all fan headers are dead, no fan running on the CPU), inserted it in a tower, added 2x256MB SDRAM, network/USB2 cards (no sound card at hand) and a 40GB HDD, installed Windows 98SE + Windows XP on dual boot, made a backup of Windows 98SE clean installation (just in case), then installed latest 3Dfx v1.07.00 drivers, PowerStrip 2.78 and Daemon Tools 3.47. And guess what? Game booted at first try! It doesn't show the 3Dfx logo but the quality is noticeably better, and detail levels menu now has normal/mip mapping instead of low/medium/high. I also tried adding SET SST_SCREENREZ=800 but didn't noticed any difference in the resolution.
So, problem is either an incompatibility with CPU/motherboard (chipset?), or the sound card since the P3 is running with no sound card. Back to the drawing board...
EDIT: as a bonus, while messing around with other old computers due to the problem above, I found a Matrox Millennium MGA G400 32MB AGP! If I'm not mistaken that's the only Matrox I own right now. I remember having a Matrox card when I was younger, I think it was (maybe) a Matrox M3D, it came with a racing game which looked beautiful, but all I can find on Google relates to Ultimate Race, and that doesn't seem the same racing game... or maybe it is, almost everything back then looked better than it looks today.
EDIT2: it's not the sound card. I removed all PCI cards, reinstalled Windows, added no chipset drivers, just 3Dfx + PowerStrip + Daemon + Tomb Raider like I did with the P3, and it still rebooted, so it's either the P4 CPU or the motherboard that causes the reboot. I just wanted to make sure the CD image worked and I confirmed that with the P3, the P4 setup just made me lose time I could have spent trying other stuff. Oh well, that's retro gaming for ya...
RETRO-W98/2K: MSI MS-6309 v1.0, P3 1Ghz, 3x256MB, GF5600 128MB AGP, VD2 PCI, RTL8139D PCI, TB400-2541 PCI, ESS1868F ISA, 160GB IDE
RETRO-WXP/7: ASUS P5KPL-AM EPU, XEON E5450 3Ghz, 2x2GB, GTS 450 1GB PCI-E, 120GB SSD, 1TB sATA