activate or deactivate a cell based on the option selected in validation list

Dear All,
I am developing a excel tool to help my job(I am working as an irrigation engineer).I know little excel and new to excel programming.

I have 2 doubts to ask you.I have attached the xls file for your reference.

1. How to display the list(created by data---Validation--list) permanently.(At present it is visible only when i click the cell).

Under the heading dripper, in coulumn 2,

2. When the unittype is selected as area and Row Plants/Trees ??? option is selected as Yes the user should be allowed to enter data in B29,B31 but should not be allowed to enter in B33.

When the unittype is selected as number (Rowplants/Trees?? can be Yes or No) the user should not be allowed to enter data in B29,B31 but should
be allowed to enter in B33.

With thanks,
Jesu