My Pentium 4 computer was running Logos 4 very slowly.
I tried the following:
I upgraded from 1 gig of RAM to 3 gigs.
I replaced the 128 Mb video card with an up-to-date video card with 512 Mb of memory.
I have read that XP will only use a maximum of 3.5 gigs combined RAM.
Logos 4 is still slower than I would like, but it is much faster than before.