Hi Plenzdorf,
What year is your laptop from? Some of the older Macs are running chipsets that aren't fully compatible with the latest versions of the AMD drivers for ATI Cards. They are especially buggy for cards that came out before AMD took over. I've got some old driver suites if you want to try, but I'll have to upload them somewhere, as they're too large to email.
Another note, is that some cards run the incorrect DX9/DX8 shader in NWN which wreaks all sorts of havoc with the game, especially when it comes to shadows. Purple and/or infinitely extending shadows are not uncommon.
Make sure that atioglxx.dll is in your NWN folder (the one with all the files in it), not your NeverwinterNights folder. You could also try finding an older version of d3d9.dll and d3d8.dll and stuffing those in there too, though that's a less reliable fix (if it even does work, I haven't had to resort to it yet.).
Are you playing on the native resolution and refresh rate of your computer? Are you running NWN in admin mode? Be sure to always start NWN with the minimum graphics settings - if it refuses to boot, run the NWConfig.exe program and reset all the values to the minimum. Make sure you pick compatibility textures too - these are uncompressed, raw textures, which are more compatible with most cards. Shiny Water and V-sync can also cause problems on ATI cards.
Last, does this happen in all NWN game sessions, or only on modules containing hakpaks? You may need to redownload/verify your CEP installation if it works fine in the OC and expansions.