You need an unbound combo box to act as a filter. Build your form with all
the data then probably the best solution is to build a tables with just the
company name. Make the table of company names the basis of the combo box.
Have the company names in the form also, but hidden. Go into the properties
of the combo and in events use the after update event (the box at the end of
the line.) Start code builder and type:
Me.filter = "[company name] = """ & me.thenameofyourcombobox & """"
Me.filteron = True
Another option would be to build a form with company name and subform with
company data.

1.  Build a table with two fields.  One column is the company name and the
other are the services that company provides.

2.  Add all the appropriate records to your table.
Ex.  Record 1 = Microsoft (company name), Computer Training (service)
Record 2 = Microsoft, Computer Purchases
Record 3 = Yahoo, Online Shopping
Record 3 = Potterybarn, Kids Clothing

3.  Create a combo box on your form with the source being the above table so
the user can pick the company.  

4.  Create a second combo box that links to a new query that uses your
created table as the source.  Include both fields.  In the criteria line
under the field for company, put in [Forms]![name of your form]![combo box
field name corresponding to the one where you have your user select the
company name]

Now your drop down on your form will only be limited to the services the
company (who your user selected) provides.