DYNAMIC INTERNAL TABLE -FIELDCATALOG?????

Hi Experts ,

I require urgent help on dynamic internal table creation.

I want to create a Dynamic Internal Table with >30 but <50 fields where the first 4 fields of the table are diffrent and all fields generated after that are of type QUAN with length 13 .i want to have the contents displayed as an ALV,wherein i dont have to declare 50 fields in the field catalog! how do i go about doing dis?

HELP Please!!!

Regards,

Goldie.