"Not responding" crashes..(big spreadsheet)

[misterboogity]

Hi,

I have a large spreadsheet with 25k rows x 50 colums, I have set
calculation to manual, each caulculation cycle requires calculation of
about 250,000 if statements and 10 sumptoducts of 2x25,000 arrays.

Each time I hit F9 the calcualtion either takes a minute or it hangs
up.

I am running Excel 2003 on a machine with 4Gb RAM -- but the memory
usage never gets above 500MB - tho excel 2003 supposedly has a limit of
1GB

Any ideas as to what is happening?

-S