Problems with cursors in applications

Hi,I'm new to Ubunto and generallynew at using Linux as OS for my Laptop.I have some problems:

  1. when using GIMP: when I move the mousecursor around in the draving area, some pixel errors get's stuck - as if the brush indicator doesn't get fully erased.
  2. in applications like Evolution & Firefox formfields: when I use the arrow keys to move the cursor around it's does allmost the same thing as in GIMP. The cursor doesn't disappear instead i have some text with a lot of vertical lines.

This is very anoying to and makes it hard to read and edit mails and...I've tried reinstalling THE GIMP and tried using KDE, XFCE and GNOME and all had the same error.I have a Dell Latitude D620, with an nVidia graphics card. I'm using the generic nvidia driver that comes wih the kernel...(I can tell you it was quite a job getting this post written ;) )I hope someone can help me.