I use KDE 4.3 on my netbook with no problems. However, it has 1 GB of RAM. I
changed the settings to work better with reduced screen size and it is
great. I used Ubuntu Remix, but don't like the look so I converted to full
GNOME and KDE.

On an older machine I would consider using Xubuntu (XFCE), Lubuntu (LXDE) or
Fluxbuntu (Fluxbox). These distros are Ubuntu with lightweight desktop
environments that should consume fewer resources, but still look great. I
particularly like XFCE.