I'm italian and we use the comma "," for decimal (es: 123,14‚¬). So excel
works with commas, but for other reason I need to input the data in the user
form with the dot (123.45‚¬). I've written a function to convert this input to
letters (CENTOVENTITRE/45, in italian of course) but it does work only if I
use the comma.

here it is:
Function EURO_TO_ITALIAN(ByVal N As String) As String

Dim TheInteger As Long
TheInteger = n
If TheInteger n Then TheInteger = TheInteger - 1
Dim TheRest As Long
TheRest = (n - TheInteger) * 100
If TheRest < 10 Then
EURO_TO_ITALIAN = INTEGER_TO_ITALIAN(TheInteger) & "/0" & TheRest
ElseIf TheRest = 10 Then
EURO_TO_ITALIAN = INTEGER_TO_ITALIAN(TheInteger) & "/" & TheRest
End If

End Function

euro_to_italian is the function that writes the letters, and that one uses
only integers (long) so has no problem

Do you have any solution? Maybe a way to substitute the dot with a comma in
the string variable would work fine.

bye