.saveas and .close methods from Access

[Marius from Rome]

My Access application opens an existing Excel worksheet and inserts data in
it.
My application should give my worksheet a new file name (i.e.
newworksheet.xls), save and close it.
I attempted using the .saveas and .close methods, but if a file with the
same name altrady exists I don't get any error while the user is prompted to
save changes in the original file.
Can anybody please suggest the best and simplest way to check if a file with
the new name already exists and/or to overwrite it?
Regards
marius