yes, then your issue is very likely the desktop environments you are using... both gnome and kde are quite heavy... on a 333mhz computer i would really consider using a light window manager...
personally, i use fluxbox:
http://fluxbox.sourceforge.net/
and my parents use XFCE:
http://www.xfce.org/
fluxbox is super light and it uses very little system resources... XFCE isn't as light as fluxbox but it's still way much lighter then kde/gnome... my parents use XFCE instead of fluxbox because it's more "comfortable" for them as fluxbox can be kinda weird for non-techie people...
oh, another light window manager is icewm:
http://www.icewm.org/
i haven't used icewm in a couple years but i know it's good... it's probably somewhere between fluxbox and xfce as far as "lightness" is concerned...
it sounds like you'd be best served with XFCE or icewm, but you have nothing to loose by giving them all a try before picking one... i think mandrake/mandriva and some of the other distros you've tried include packages for all of these window managers...