I just installed KDE 4.3.3 in PCLinuxOS on a Dell Dimension 4700 with an ati radeon x300 video card. Every time I login plasma workspace crashes. After I close the bug report screen the desktop comes up, but I am not able to activate desktop effects and things run much slower than in KDE 3.5. I changed the accelerator from XAA to EXA as specified in other forums. That sped things up a tad (not as good as KDE3.5), but I still can't activate desktop effects. I filed a bug report and reported this to the PCLinuxOS forum. I noticed that others have had the same problem. Has anyone been able to solve this?

What's this accelerate or stuff? An X11 configuration or somewhere in KDE's settings? I have a similiar problem sometimes too, but it's temporarily... the reaction time is ultra slow but when changing screen (strg+alt+fx) and changing back again it moves again for a second... restarting kwin and plasma-desktop works most times...

The desktop effects don't run at all or are they slow (and the system tells you that they were disabled for that reason)?

If you simply can't check the box in systemsettings your video driver doesn't have 3d-acceleration enabled.
glxgears may help to check that...