Are you using V2 Beta or V1. If you are using the version 1 SPS, you should be
able to navigate to the documnet using word  and check  it out from with in word.
Is this not what you need?

Not if you're using Word 97. Later versions of Office support
SharePoint's versioning I believe...

Yes that sounds correct.
With the sdk, you can do quite a bit. I have done something like this with an
xml editor. Basically, I added menu options to open  from the repository. This
brought up a "File Open" form that would let the users see the library as a
treeview not unlike an explorer view. They could then open the file. The sdk
code would go in check  the status of the document  and do a check out if needed.
Then copy the file to a local directory and had the xml content editor open it
from the tmp dir. This is obviously a slimmed down version of the tool, but I
suppose that you could do the same with Word97.

Well, thanks everybody for your help

I have a SPS 1 and Windows 2000 with office xp

The option for ¡°check-out¡± from office doesn¡¯t exists (in the document
opened from the portal, because if I open  Word from the desktop, and save a
document, the option did appear)

I will try to do it from SDK.

I hate to be simple, but it sounds like you aren't using an enhanced folder.
Are you?

As a matter of fact I can use a check  out from a Web folder, even from Word
itself

But if I open  the document  from the sharepoint portal, word  opens but this
option doesn't show.

Apply service pack of office xp and also of sps and check,

The only option with SPS 1.0 is to install the Client Tools (available on the
CD). Once installed, a user with Word and the client tools can open, edit and
save the document  to the portal directly in Word.