well i can say that it won't worth the money you spent to a new second hand pentium 3 600mhz cpu

running for linux it may be enough but general concerns for todays computing world needs at least a athlon 64 or pentium 4

anyway if you gonna use it for office products (openoffice.org etc.) it is enough for you but watching movies or playing anything by building up a network is a dream almost with that 4mb pci graphics card

my suggestion is saving money change it completely when you need to but for now don't do anything more than the cpu upgrade you have done