Samsung Galaxy S : Why can't I set cursor position in text boxes in browser?
Press and hold the ?123 key at the bottom, left corner of the standard Samsung Galaxy S keyboard. The keyboard switches to a four arrow cursor pad that you can use to move around a text field. There's also a delete key, select, cut, copy, and paste; click the Text key to switch back into keyboard mode.

This works with just about all text fields in all applications that I use.