There are three options:
1. You can limit the entry in the field to the visible area (hence all data is always showing). There is a checkbox in the Object palettere for this.
2. You can have the text shrink to fit the size of the available space. If you change the font size to 0 in the Font palette for the value property. The issue with this one is that the text could get to an unreadable size.
3. Build the form to be dynamic and allow th efield to resize itself to fit the text entered. There is a good example of this in the samples that are shipped in Designer. Lok in this location and pay particular attention to the Comments field. In th eDesigner install directory:
EN\Samples\Forms\Purchase Order\Dynamic Interactive\Forms