Pc3200

Should a Tyan S2720 [Thunder i7500]) work with a mix of existing 2x512MB
PC2100 CL2 ECC REG and new 2x1GB PC3200 CL3 ECC REG?

Or at least with the existing 2x512MB PC2100 CL2 ECC REG and new 2x1GB
PC2100 CL2,5 ECC REG?

Background:

My S2720 runs without problems with 2x2GHz Xeons and 2 x 512MB Infineon
HYS72D64000GR-7-B (PC2100R-20330-B1, 512MB DDR 133MHz CL2 ECC REG).

Now we want to extend memory by 2GB. We tested 2 Infineon
HYS72D64300GBR-5-C (PC3200R-30331-C0, 512MB DDR 400 MHz CL3 ECC REG) but
this was not sucessful - mixed with the existing memory as well as
installed alone. The server did not even start but beeped only on power
on. There is of course a slight chance that the new modules are defect.

Is PC3200 in general coampatible to PC2100? Does the S2720 not like the
CL3 of the new chips? Any other reasons why the new modules won't work?

I could get Kingston KVR266X72RC25/1024 (1GB 133MHz DDR ECC Registered
CL2.5 DIMM, x4 ). Should these work on the S2720 along with the existing
Infineon modules?

Klaus