Mapping the BP fileds

Hi,

I am working on the SAP R/3 4.6C and CRM 4.0.

We have extended the BP transaction through EEWB.

and also the KNA1 table by append structure.

I have a small problem.

I have a custom field in BUT000 which is of length 54 and i need to map this with the Field in KNA1 which is 18 chars.

How can i achieve this?

Could any one pls advise.

Thanks.

Muraghendra D