ext3 is the best out there, it does fragment but to such a tiny extent it is practically zero, but windows doesn't directly support it - hence the link in jerioc2day's post - and from a quick google it looks like mac doesn't support it directly either
so ntfs is probably the best bet after that, but does become fragmented, and with a large disk you don't want the hassle of defraging it
the network share idea would work, but you said you would be using 4gb+ files, which would be slow to transfer across a network
amd athlon xp 2600+,1280mb,FX 5200 128mb,200gb & 120gb,xp pro sp2