HTML Validation Service - Better Explanation/Link - What document types?

I went to validate my page (http://cr915983-a.hnsn1.on.wave.home.com/) and
got the following (see below).
When clicking on the "explanation" link
(http://validator.w3.org/docs/errors.html#attr-undef), it says "This is most
commonly caused by using vendor-specific attributes without setting the
document type appropriately."

What I would like to know is, can you put a link at that spot to the
available document types so that I can set it properly? I would like to be
able to have the MS "hidefocus=true" on my page, and also have it validate
correctly. Which type should I use?

Thanks,
    Shenan

-----------------------------------
Document Checked
  a.. URI: http://cr915983-a.hnsn1.on.wave.home.com/
  b.. Server: Microsoft-IIS/5.0
  c.. Content length: 3463
  d.. Character encoding: unknown
  e.. Document type: HTML 4.01 Transitional
Below are the results of attempting to parse this document with an SGML
parser.

  a.. Line 42, column 14:
   <a hidefocus=true href="?page=Login" target=_top><img alt="Shenan Haw ...
                ^
  Error: there is no attribute "HIDEFOCUS" for this element (in this HTML
version) (explanation...)