Corrupt Spreadsheet and Temporary files

Morning all,
I have searched for an answer before posting this thread, so apologies if this has already been covered.

I am an average user of Excel 2003 to manage a 1.7mb shared workbook, from which 40+ users input data. I have 3 main serious problems:

1) Although shared, occaisionally I get the message " the file is locked by USER, please save with different file name

2) At least twice a week, my workbook becomes corrupt and a series of weird files appear next to the Original file. These files have no extension, no description, they look like temporary files, but do not delete themselves, always 8 characters in length, a mix of numbers and letters.

I delete these files when they appear, remove the sharing, save the file, then share it again to prevent corruption, but 2 days later, same happens again. I am unable to open the original spreadsheet, but if I click on one of these weird files, it opens up to my workbook????

3)when I remove sharing, a number of users appear in the list, but are not actually in the file. Or the same name will appear twice with different dates.

I appreciate any thoughts you may have with these issues.

Many Thanks

Jet-Leon