combine worksheets

Urgent!!

I need a formula to check, match, found and autofill data in two different sheets.
I have used the following formual on my master sheet:

IF(ISERROR(INDEX(Sheet2!K$8;K$144,MATCH($E8,Sheet2!$E8:$E$144,0))),"NO COMM",INDEX(Sheet2!K$8:K$144,MATCH($E8,Sheet@!$E$8:$E$144,0)))

It seems to work, but my problem is the following:

I've got a master file with account numbers and ref numbers in columns E and F and the surnames and initials are in columns G and I.

I receive a monthly summary from head office on sales done and comm earned in a text format. To open the sheet in excel, and then "column to text" is no problem.
I've made my master file the same as the text file for easier refences, although my account numbers are numerical.

The problems I'm experiencing on the moment is:
1. If I receive commission on the same client in more than one row it does not add up in my master file, maybe I should use COUNTIF in the formula

2. If I receive comm on a client which for same reason does not appear on the master file, this is also not included in the commission column on my masterfile.

3. I then furthermore need exception reports when I compare the different months and commission sharing % from say Jan to Feb in the master file.

Do hope someone will be able to assist me!!

Thanks Ronette