RDRam puzzle

I have a Dimension 8100 and it uses rdram. My OS is ME, don't know if that
matters.

I bought some memory upgrade. I only had 128 MB, so I bought 512 MB.

My question is, the 128 is 600-53 (nonECC). I'm guessing that means it runs
at 600 Mhz. The 512 is PC800-45 (ECC). 800 Mhz I'm guessing.

Should I leave the 128/4d nonECC 600-53 installed or will it slow down my
512/8 ECC PC800-45 too much?

I don't think you're supposed to mix noECC with ECC either? (I meant to buy
nonECC but musta picked the wrong one by mistake. I bought them online, so I
really don't want to go thru the hassle of returning them if I can still use
them without causing any harm.

What's the best way I should configure this?