In Microsoft Office Excel a long text string is readable over multiple columns whenever the next (right) column is empty. Is that also possible within Google Spreadsheet?
That's only possible when you're using the new Google Spreadsheet:
and now with text in column B:
Read all about the new Google Spreadsheet in this official blog
If you do not want your text to overflow use Format > Text wrapping > Clip. This will work even if the next cell is empty.
If Format - Text wrapping - Clip isn't resolving your issue, try:
Select All (Ctrl+A or Ctrl+Shift+Space) and Ctrl+/ to Clear Formatting.
Can be also done from the Format menu (at the top), choose the last Option, Clear Formatting.