Add character to a field name with special char's

Hi,

I new to this forum and havn't done alot of Javascript.

Could some one tell me how to do this

I have a text form field with a '*' in it
<input name="mail_subject*" type="text" size="40" maxlength="50">

I want to add a word like 'subject' to the front of the field like this

document.contact.mail_subject*.value = 'Subject - ' + document.contact.mail_subject*.value

but it doesn't like the * in the field name.

Can some one tell me how to do it.

Thanks