[G4] ram question

[hec]

hi,

i have a mdd dual 867 and i would like increase the ram by 512 mb.  i 
have a few questions.  are there different makes of ram, if so does 
the quality and reliability vary?  are there companies that group 
members find to be better?

according to the specs at the apple site this machine says that is 
machine can use pc2100 or pc27oo memory (there is a single 256 mb 
pc2100 in it now).  what is the difference between the two types and 
how do they influence how the machine works?

i appreciate information to help me make this decision.  thank you all.

hec