Hide/unhide columns based on the drop down list value

Hi,
Need help.
Using Excel 2007 would like to create a worksheet that will hide/unhide certain columns based on the text selected in a drop down list.

The purpose of the document is track company personnel individual trainings.

Employees holding different positions need different trainings. That’s why I’d like to create a spreadsheet that will help a user to choose what training is required for a person holding a certain position.

For example, I have 25 employees and 6 positions in a company. Positions are: A, B, C, D, E and F.

Each position has specific training requirement. Let’s say there are 7 trainings: tr1, tr2, tr3, tr4, tr5, tr6, tr7.

Employees holding position ‘A’ need to be trained on tr1, tr4 and tr5
Employees holding position ‘B’ need to be trained on tr1, tr2 and tr6
Employees holding position ‘C’ need to be trained on tr2, tr5 and tr7
And so on.

So, what I’d like to do is when position is selected in a drop down list, required trainings will appear and unnecessary ones hide.

Sample spreadsheet attached.

Following scenario:

Column A – Employee name
Column B – (drop down list) – position of employee
Columns C to W – are trainings. Each training 3 columns.

If position selected from drop down list, let's say position 'B' then unhide - tr1, tr2, tr6; hide - tr3, tr4, tr5. tr7 ... the same scenario for other positions.

The form is there but i do not know how to make it work.
Please help.

Thank you very much in advance,

Vagif