You are using unpublished or forms that are one-off for some other reason.
Outlook 2003, Outlook 2002, Outlook 2000 SP2 and Outlook 2000 or 98 with the
Email Security Update will not run code on one-off forms; see
http://www.outlookcode.com/d/secforms.htm for more information on this
issue.

To ensure that a form does not one-off:

-- Make sure the "Send form definition with item" box on the (Properties)
tab of the form is *not* checked. [1]

-- For in-house corporate use with Exchange Server, publish the form to the
Organization Forms library or a public folder's forms library, as
appropriate for your application.

-- For collaboration via the Internet, publish your form to your Personal
Forms library. Save it as an .oft file and send it to other people who need
to use it with instructions to publish it with the same form name that you
used.

Many other things can cause one-off forms. If the above steps don't work on
a new item created with your form, see
http://www.slipstick.com/dev/formpub.htm#oneoff for other possible causes.

[1] Whenever you publish a message form, Outlook will suggest that you may
want to check the "Send form definition with item" box to ensure that the
recipient will have the form, especially if you're sending to someone via
the Internet. In the current Outlook security environment, this suggestion
is obsolete. Ignore it unless your form has no code behind it.

forms don't work, anything that is referenced on the outlook form in the VB
script i.e. a button or a combo box etc does not work i.e. my submit button
does not work etc.

What doesn't work, the code in the form? Is the form published on those
other systems?

There should be nothing inherently that would be different for systems
running on WinXP and Win2K if they are running the same versions of Outlook.

forms don't work, anything that is referenced on the outlook form in the VB
script i.e. a button or a combo box etc does not work i.e. my submit button
does not work etc.