a question about ram upgrade (crucial)
 

I've got 256mb of crucial pc2100. I'd like to get another 256, problem is I
can't seem to find the exact same module through any of the usual sources
including crucial.com
There is a small difference between my module and the available upgrade
module, the organization of mine is 64M x 64 bit, the upgrade is 32M x 64
bit.
Am I just splitting hairs here, does it matter?
What should one look for when upgrading? Same brand? Same bandwidth?
I have a pretty smooth running machine and I'd hate to mess it up.
thanks for any advice