How can I stop Excel2003 from automatically detecting and formatting a cell?

I downloaded some account information as an Excel file (only option
available). The financial institution shows the dates/times as this:
"5/30/2008 2:44:23 PM"

When I open the file, dates and times for March have the exact same format
as the webpage (5/30/2008 2:44:23 PM) and the cell is treated as "general".
But dates in June are displayed as "06/01/2008 20:44" and the cell is treated
as "personalized".

I want the June dates to be treated the same as March dates but nothing
works. If I change the cell format to "text", the content becomes a weird
number: 39453.7503472222. Same if I copy and paste the info into a
pre-formatted text cell. The only thing that works is to manually copy and
paste each value (using F2) but this is highly inefficient.... or doing a
bunch of search and replace in notepad.

Is there a way to prevent Excel from automatically detecting cell formats?
Thank you for any help you can provide