Specify which rows to NOT hide, and have excel hide the rest
 

ok, before i start working on my excel sheet,
I'd like to specify in some how in some way,
(pop up window, or entering a number in a cell, it doesnt matter as long as
its "excel-newby-friendly")

A range of rows i wont be using, and have it hide those rows.
(or, preferrably, i'd like to specify which rows I WILL be using, and have
the script auto-hide the rest.)

In Column A, the cell values a "A-1" through "A-20"
after A-20, the next cell's value is "B-1" through "B-20", and so forth, up
to "O-1" through "O-20"

those cell values never changed. i use them to identify the rows in my sheet.

anyhow,
So before i start, the question is asked:
USING ROWS(to input data): A-1 through A- [x]
B-1 through B- [x]
C-1 through C- [x]
(and so on, up to
O-1 through O-[x]

The [x] indicates where i'd input a number
(if it can have a default number, like "2", that'd be awesome)

SUBMITTING this information would have excel HIDE every row not specified
within that 300 row range.

So... lets say i said
USING ROWS: A-1 through A-[5]
B-1 through B-[10]

This would make the rows with Cell's A-6 through A-20 HIDE, and rows with
cells B-11 through B-20 HIDE.
(Well, reastically, i'd also be specifying which of the "C- " , "D- ", etc ,
rows to also not hide...but i think you understand)

If it can't be done this way, i'm open to any other methods of accomplishing
this..
TIA