Concatenation in Excel 2003

Hi, I'm having an issue right at the moment, and I wanted to see if anyone encountered this and has a suggestion. I'm trying to concatenate 2 columns in Excel to create a username column. Our username format is the first initial of the first name and the first 7 letters of the last name. I have 2 columns in my workbook, first name and last name. I do know how to Concatenate the full data of each of the cells, but i wanted to know if there's a way to do just parts of each cell, by taking the first character of the first name cell, and the first seven letter of the last name cell.

Any ideas?

Thanks in advance!