tiger runs but its sluggish your best bet is to go with panther ( 10.3)

its older then tiger but peopel are undoubtedly dumping it giving you a bargain its stil modern enough to be able to run along and it wil run in 128 mb

or you can go to os 9 but then you have the problem of scrounging for modern software ituns supports for 9 stops at 2 the only classic browser that is stil supported is icab and so forth

if you want to go with os 9 go and get it i am sure you will be happy with it

but if you want an easier time of it regarding software security pre emptive multi tasking protected memory and al thos other wonderfull os x features that mena nothing to us but make it a fine os then os X is your best bet