In the version 4, we can't add a decimal number column with the create table forms.
I just did, and it worked for me.
What exactly are you trying and where does it fail for you?
In the GUI, I found the following column (I translate from french to english): PK, Name, Data_type, lenght, not null, default, comments.
In the lenght field, if I enter 9,3 to have a NUMBER(9,3), I have a message saying that the number must be an integer.
Switch to the advanced view, go to the data type panel on the bottom, and set precision and scale.
Ok I see. By default we only see the tabs on the bottom. I can now see what you see and now it'obvious.