Darn it, I'm late on giving my answer of the RAM being defective.

Unless your motherboard ONLY supports DDR400 and upwards (which may not be likely in your case), it would surely work with DDR333, UNLESS....

1) The DDR333 RAM is defective (this can happen on brand new RAM)
2) The motherboard works with only physically single sided RAM or Double sided RAM modules.
3) The CMOS RAM parameters are manually set to incorrect value(s).

[On a slightly different tangent]
You'd think in this day and age that RAM type incompatibilities would have disappeared.
Not so.

You'd think in this day and age that Harddrive incompatibilities would have disappeared too.
Not so.

[Ram]
Just built 5 brand new workstations and found one 512 RAM module defective in the 312MB area. Because a 72hr burn-in procedure is performed, the memory error was found before it shipped to a not-yet-frustrated client. (when replaced with a double-sided memory module, it would not boot)

[Harddrive]
Just built the Server for the 5 new workstations and found a Maxtor 300GB (or less) SATA drive has random disk errors (issues) with a motherboard with an NForce4 chipset, in either a single or RAID configuration. A HD firmware upgrade from Maxtor (supposed to fix the problem) doesn't, but I figured out a work-around for the future and simply replaced the Maxtor with a WD on this particular machine.

Years ago, there used to be alot of incompatibilities between products whereby a tech almost had to memorize a list of them.

But as the saying goes: "The more things change, the more they stay the same."