very simple Perl or VB script needed

I need a very simple script. The MAXIMUM BID I can accept is $30 This should not take more than 25 minutes to write. I have a text file which is a matrix of data. It has n rows and m columns, call it O for original. I need a perl program (with GUI) that inputs this matrix and outputs a new matrx, call it R for reduced. The problem is that I am inputting this matrix O into a program which can only accept a maximum of 100 rows. So I have to reduce the number of rows in the following way. Suppose n = 25000. I want to take the first 250 rows and create a new representative row which is just the average of each column for those first 100 rows. Then do it for the second 100 rows and do the same thing. If n=35000 then the every 350 rows would need to be colapsed into a single representative average row If n=350 then then every 4 rows would need to be collapsed into a single representative average row (every 4 not every 3 since the maximum I can have for R is 100 rows). I want a gui where I can select the file and save it with another name. The file that contains O is a .txt file and the output should also be the same type.