[SnapleFlapintosh]

Hello,
I recently maxxed out the RAM on my Graphite iBook 466SE, which meant removing the 256MB module which had previously been in there.
Wanting to put this freed-up resource to good use, I tried installing it in my mother's 333mhz, tray-loading iMac, but the machine couldn't recognize the RAM, regardless of whether it was in the upper or lower slot. Next, I tried installing the RAM in my girlfriend's Compaq Presario laptop (I think it's a 300XL or something), which also proved fruitless.
The confusing thing for me is that both the iMac and the Compaq require 144 pin PC100 RAM, which is exactly what I've got.
So, two questions:
1) How the heck are we supposed to know what RAM will work in which computers, when most vendors don't give you much more info besides the number of pins and whether their RAM is PC100, PC2700, or whatever.
2) Does anybody know specifically which Macs or PCs out there would be able to happily accept and work with my spare 256MB? I ask this because if I sell the thing, I want to be able to tell the buyer whether it has any chance of working in their machine. Also, I'm thinking maybe if I stumble across somebody whose computer is in need of a RAM upgrade, and I know mine will work, I might just give it to them. Lastly, I figure I just might luck into some unwanted old Mac that somebody's giving away free or cheap and that might suddenly become useful if I were to put that RAM in there.
Thank you so much!

[ftaok]

I'm surprised that you actually got the 256MB chip into the iMac. The iBook takes laptop memory and the iMac should take desktop memory. The only iMac that I know of that takes laptop memory were the G4 iMacs.
As for determining RAM types, go to Crucial.com and use their RAM selector. It'll tell you what type of RAM is required and also if special needs are required (such as RAM matching, etc.)
ft