How to read a .TXT-file line by line?

I would like to read the first line of the .TXT-file,
Perform some action on the read data (the .TXT-line)

Read the next line - perform some action
Read the next line - perfom the action again
etc...

Until all lines of the .TXT-file is read, and the action is performed on
all lines (imported data)

My problem is that I have a HUGE .TXT-file of almost 3.000.000 lines!!!
I'm aware that going through all these lines, one-by-one, will probably
take a week or so, so I have to make my first test-program read a
smaller file, until I'm sure it is working.

But, how to read the file, line by line, in the first place, since I
can't import such a huge file in my trusty old XL2003?

Oh, I case you wonder what the 'action' is, I want to remove those lines
in the .TXT-file that doens't fullfill certain criteria, thus (hopefully
:-) ending up with a .TXT-file of only approx. 105.000 lines, which then
can be converted into a webtable.


Thanks in advance...

CE