Malte - at least some of Dell's newer servers use the Intel i840 chipset, which only supports RAMBUS memory. Though prices on this have dropped, the last time I checked (which admittedly was a month or so ago) it was still about 3x as expensive as SDRAM PC 133. Dell's memory prices have never been good, but it's not as bad as you might think from the raw comparision.
Well ,,, it is as bad but not just because it's DELL, you gotta factor in the "RAMBUS sucks" numbers.