It sounds like you have got a setting mixed up. Comma is used in some countries to mean the decimal marker. (Other countries use the full-stop or period).
So in Germany 23,500 means 23 and a half (and a question why you put 2 extra 0).
IN England & US, 23,500 means 23 thousand 50 hundred.
In Excel, if you want to show the commas (meaning separation of the 1000 units), go to Format/Cells/Number and tick "use 1000 separator"
Then enter "23500" and it will be shown as 23,500 (or 23.500 if you are using comma as the decimal marker)
You might also have the cell setting showing extra decimal places, so the 969,000 might be using the comma as decimal marker, and 3 decimal places. Again, go to Format/Cells/Number and select the number of dec. places you want. Try "2" and if this changes your 969,000 to 969,00 then you're definitely using comma for the decimal place.
Edit: just seen your question clarification
In Excel 2007, go to Excel Options (the big round button, then the bottom of the menu) / Advanced section, Editing Options and find the setting "use system separators". Clear the Use system separators check box. Type new separators in the Decimal separator and Thousands separator boxes.
In Excel 2003, Tools / Options/International tab.
Under Number Handling, clear the Use system separators check box. Type new separators in the Decimal separator and Thousands separator boxes.