equipment naming problem...........,

hello all,

my client wants the equipment name with only chars.. that must be less than six charecters. and alphanumeric should not be allowed.

for this what i need to do in configuration part.....?

and i have set the number ranges A - ZZZZZZ but it allowing,if i gave ABCDEFG ..?

so what i have to do .............

please help me in this regard.....,

thanks in advance.