Ahhh... I misunderstood the question. I didn't see the "letter wizard"
part. I thought the OP was asking how to get his/her template to appear
on the "Letters & Faxes" tab under General Templates.

Charles Kenyon wrote:

Unless the template's name contain's "letter" it won't show up as a wizard
option even if in the Letters and Templates folder. If it does contain those
characters, it will show up even if in a different sub folder of the User
Templates or Workgroup Templates folder.