[G4] clam av and hard drive question

[dapper dan]

any help installing clam av software is appreciated.i downloaded and cannot 
figure out what to do next.

also,how much bigger an internal hard drive can i throw in a g4 powerbook 
867mhz powerbook?i have 30 gig.is 80 possible? any advantage to an internal 
over external one?one more question.can i buy an internal/external drive 
that spins at a higher rate than the one that came with the powerbook?

thanx for the help from a recent macc newcomer

dan