64mb is extremely optimistic
presumably the ram is very old as well, as would be the hard disk
128Mb may be fine also, but at less than 256Mb "top" will show fairly clearly there is a lot of swapping going on. once you kick in any mysql and php activity the machine will start to swap more and more become unbearably slow with only 64mb, 128 will be ok with 1 or 2 users. 256Mb with 5 users is so-so, but 512 and sme starts to get cracking.