Easist way wud be to open the file in 2003 and see if the format is correct there. Normally, if the date format is correctly made, then there will be no problem even in 2007.
In the alternative
First copy the date column as u received it in another column/sheet. the select the entire range of dates and u will get a error pop up. in that the various correction options would be available. Select convert to number if available. if all the formats are correct, then all the cells will get converted ito the corresponding numbers representing the dates. Once it is done, select the data again and format it in any way u want. If the date format is originally wrong, those cell will not convert to numbers. Before re formatting corret only the ones which have not converted to numbers and repeat the re formatting. This should solve the problem