Multiple Master on XP without ATM?

No and since MM fonts are pretty much a dead format you should probably 
start considering an alternative.

The only official and safe alternative, at least for the Multiple Master fonts
in the older versions of the Adobe Type Library, is to use the OpenType versions
of the same fonts. For each of the Multiple Master typefaces, Adobe made a
corresponding OpenType font corresponding to each of the pre-defined instances
of the Multiple Master font. Obviously, you no longer have the ability to define
your own instances (in fact, one of the reasons for the demise of Multiple
Master fonts was the reality that exceptionally few users of these fonts used
anything other than those predefined instances).

“Conversions” - assuming that the license for the fonts you have licensed allows
for such - are always problematic in terms of what you get being fully
consistent with what you had. For better or worse, given all the advantages of
OpenType technology, you would be best off to migrate to that as soon as
possible.

Some Adobe apps (such as ID and Photoshop) bypass the OS's font handling and you
can use MM fonts in these apps by placing them in the Adobe fonts folder. You
get access to the primary instances but you can't create custom instances.

Various apps can convert MM instances to Type 1 fonts. The main font editors can
do it, FontMinder could do it, TransType or CrossFont (or possibly both) can do
it, and there was even a free font editor (Noah) that could supposedly do it,
though it used a different naming convention, which made it harder. However, you
have all the usual issues associated with converting fonts (licensing, lossy
conversions, unwanted substitutions, etc), so I agree with Dov that OT is the
way to go.