Got a dell i'm just upgrading for a friend, it has 2 x 512mb of samsung Pc2 5300 code - M378T6553CZ3 - CE6

I can find plenty of some cheap Samsung memory on ebay but most of it is coded - ............CZS - CE6

Both appear to be CL=5, non ECC, Unbuffered, DDR2-667, 1.8V, 64meg x 64

To save him money I want to upgrade it to 2Gb but use the two empty slots so the question is do you think they will mix?

PC5300 has always been a bitch. HP use it a lot on older PC's.
I've got a bucketload here if you need some.

shouldn't be any compatibility issues with that.
it should generally all interoperate. I would match up the 2 new sticks as a pair though, i.e. in the two currently unoccupied slots.

keeping to the same manufacturer should help but there is generally not any issue mixing brands as longs as the specs match.

Cheers guys