90% this is caused by something running in the background.
Okay let's try some standard things.
1) Rename the AVI folder to AVI_back
2) Set the color depth to 16BIT
3) Turn off everything in the background like E-mail/ICQ/Messenger, Virus protection and everything in the system tray beside the clock.
For you especially #3.
If that does not fix the trouble we will look at your refresh rates.
Okay let's try some standard things.
1) Rename the AVI folder to AVI_back
2) Set the color depth to 16BIT
3) Turn off everything in the background like E-mail/ICQ/Messenger, Virus protection and everything in the system tray beside the clock.
For you especially #3.
If that does not fix the trouble we will look at your refresh rates.