chifu,
In addition to checking out the amount of MEMORY on your user's PC, I would suggest you also check out the following possibility...
Some spreadsheet users do not appreciate that spreadsheets can (and often SHOULD) be set up as a type of "database".
A typical "database", for example, would have field names like: Date, SalesPerson, Quantity, Price, etc, where the data is entered "vertically".
The "newbie user", on the other hand, enters data "horizontally", with an additional "block of field names" for each "time period". For example, if the user wants a "Weekly" or "Monthly" report, then they would repeat the "block of field names" for EACH Week or for EACH Month. Such a practice is not only "inefficient", but as in this case (possibly the case), the user soon realizes that there are only 256 columns. Excel has, on the other hand, 65,536 rows.
More importantly, however, there are "built-in" "database functions" in Excel. They aren't anywhere nearly as powerful as those of Lotus 123. However, they are still powerful, and should be used.
There are "Data - Filter" options, but also "Data - Filter - Advanced Filter" options. It is the "Advanced" Filter options that allow the user to "extract" data from the one (database) sheet to another sheet where "selective" data is captured to produce the various reports required.
These various reports can be for a specific period, by specifying "criteria" which specify the "start date" and "end date" of the records required for the report.
Similarly, reports can be generated to include all the sales for a particular salesperson, etc.
An alternative to producing reports that contain all the records, is to produce a report with just the "totals" - i.e. a "matrix" of totals by salesperson by month, for example. This is accomplished with "database formulas".
Another option is "Pivot Tables".
If you feel that your user has gone off on "that other direction", and could benefit from re-shaping the file into a "proper" database type of spreadsheet, then please feel free to ask me for an example file or two. Just email me, and I'll return the file(s) via return email.
Regards, ...Dale Watson dwatson@bsi.gov.mb.ca