WOW - New Graphics Card or more RAM?

[Quark]

The old original 512 MB RAM chip that's currently installed in the computer is labeled as follows:
Infineon 64Mx64 SDRAM (16 chips, 8 on each side)
PC2100U-20330-B1
512 MB, DDR, 133 MHz, CL2
Now, this is "Double Data Rate" DDR-RAM (184 or 186 pin module respectively), so I assume that both the label "SDRAM" and "133 MHz" on the sticker of the RAM are somehow an old description (from the year 2002) but actually mean "PC266".

SDRAM = "Synchronous Data Ram". Almost any computer RAM you see now is SDRAM, whether or not it's mentioned. It uses the same methodoly as RAM chips have been using for years, replacing the EDO and Fast Page RAM styles. The chip is really a "DDR-SDRAM" chip.

But even when we've removed that old RAM chip and inserted i.e. a new Kingston PC266 (PC2100) 512 MB "ValueRAM" module, the system hangs at power-on with a ring tone. We've also tried all BIOS options available for the 400 MHz FSB ("Auto" (set Memory frequency by DRAM SPD data), "2.66" (Memory frequency = Host clock x 2.66), "2.0" (Memory frequency = Host clock x 2.0)).

Have you tried underclocking the RAM at all? Just to see if it will boot? Are there any settings for memory timings? Settings like CAS, tRCD, tRPD, tRAS. If there are, try setting them really high (slow) and see if that works.

Or are the PC266 modules being sold today de-rated PC333 modules which won't work with a 400 MHz FSB anyway?

It depends on the memory chips on the stick. There are many RAM chips out there right now, but all follow the same philosophy as CPUs: stringently test them at higher speeds, and if they fail even in the slightest, mark them at a lower speed for selling. The reason overclocking is a hit or miss affair is because the vendor's tests are much more aggressive than normal usage.

I'm confused as to why anything labeled DDR-SDRAM would not work in a system that supports it, since the fundamental technology hasn't changed at all, just the speeds it runs as. New systems may or may not use DDR2, but that's a whole nother ballpark and those wouldn't even fit in your memory slots. It may be that you have a finnicky motherboard in general. I used to have one of those, and it sucked. You'll have to do a huge amount of research into what chips have worked with your motherboard in order to upgrade, if that's the case.