I am working on a 10 column Excel (vs. 2004/Mac OS X) spreadsheet originally created
by someone else. I need to add new data while retaining the original info.
When I attempt to add a new row across all of the columns, a thin, gray
frame/window appears around a section of the spread sheet and limits the new
row to only 3 of the 10 columns. What is it? Is it a filter? How do I remove it without
losing the data in the section it surrounds?

Try selecting the ENTIRE row, place the cursor along the far left (over numbers, you should have an arrow pointing RIGHT), then RIGHT-CLICK, and chose INSERT (Insert Row Above or Insert Row Below in office 2007).
The default is to add a row ABOVE the selected row.
Excel should adjust any formulas to account for the new row.

thank you, Thaylok.