In rare instances, the blinking cursor has been known to cause seizures for sensitive clients.
You can effectively stop the cursor from blinking by using Regedt32 to navigate to:
Double click the CursorBlinkRate in the right hand pane and set this type REG_SZ value to 999999 milliseconds.
At the next logon, the cursor will stop blinking.
NOTE: A visitor has reported that -1 also works.