Cast in sql

i have a column in sql sever declaring as float.
and there are times i wanted to insert the word : N. A into the column..
wat is the right expression for inserting the char?

ie
Insert xxx Into xxx values(' " & Cast ( 'N.A' As float) & " ')
this the above statment correct?..or do i omit commas or colon etc? thanks

In a float field you can't store chars. You can mark some records by leaving the field blank, <NULL> , or by putting a special value in it (-666.111222333).