"What I have done is take the HD out of a Toshiba Portege 3490CT. It is maxed out at 256M ram and has a 600Mhz P4"
there is not a P4 at 600 mhz, maybe 1600mhz
doing a search on your laptop, i found it has a pentium III at 700mhz, slow would define it(for today's standards)
lxde or puppy linux are options for this slow speed cpu
i have used pclinux 2009.1 in a PIII at 650mhz and it was slow but in livecd most systems are like that, slow
in the model you mention the maximum of ram allowed is 256 but sometimes the system will take more, you will have to try with another module to see if it accepts it
i know that some users want to use as long as possible the hardware they have but sometimes the problems that creates this kind of attempts are more than the benefits it offers
this one looks like it should keep running win 98 or xp with all set to minimum