memory question

[HighTich]

I have a dell laptop and want to upgrade the memory, the specifics say to use a PC2100/266mhz DDR. Right now it has 2 slots with 128mb each.
I was gonna buy 2 sticks of 256 for each slot, but this guys at Fry's advised me to buy this PC27000 512mb /333mhz stick since it was on sale and would save me money, he also said it should work with mine even tho its 333mhz and not 266mhz. Well, I bought it since he sound convincing and added it to the 128mb so now I have 640mb.
So far its running ok and reads the memory, but just to have piece of mind. Is what I did ok? and will it not ruin the laptop? Can I mix match those 2 memorys?

 

[imported_brad]

i THINK what your comp will do is just automatically run the faster memory at a slower speed...it should in a sense, underclock it. Ive heard of people doing that before.

 

[Terumo]

Not adviseable. Different timings. And usually it'll work at only the slowest memory speed.