[G4] novice question re leopard

[hecowan]

hello group,

i'm a novice user with a dual 1.25 g4 and am about to upgrade to 
leopard 10.5 from 10.4.11.  one of my concerns is how to update the 
external drive i use to backup my information.

my understanding is that external drives requires a different type of 
formatting for leopard than the earlier os x systems use.  what is 
the easiest and safest way to make the external drive compatible with 
the leopard on my work machine?

thank you for your time and assistance.
hec
mdd 1.25 dp 10.4.11