This is probably late, but since I'm also creating a kitsune for a game I'll state my opinion on it. The Alternate Form ability specifically states that it functions as Alter Self, and from SRD it states;
"When the change occurs, your equipment, if any, either remains worn or held by the new form (if it is capable of wearing or holding the item), or melds into the new form and becomes nonfunctional. When you revert to your true form, any objects previously melded into the new form reappear in the same location on your body they previously occupied and are once again functional. Any new items you wore in the assumed form and can’t wear in your normal form fall off and land at your feet; any that you could wear in either form or carry in a body part common to both forms at the time of reversion are still held in the same way. Any part of the body or piece of equipment that is separated from the whole reverts to its true form."
Ergo, any equipment you are able to 'wield' changes to fit your new form. Quadraped states that the kitsune isn't capable of wielding weapons (so these would blend into your 'body' and become nonfunctional) while armor is still fair game. Therefor, whenever a kitsune reverts to his true form, his armor merely changes to accommodate his new form (in the fourth edition version of the class, seen in the actual magazine, we're gifted with a wonderfully drawn picture of a kitsune wearing a cape. I imagine an armored fox would have something similar, perhaps instead being a bangle or some such, perhaps even a tail ring, that grants 'magical' protection' equal to the Armor's AC). However, I may just be mistaking the term of 'wearing'. As a kitsune, there's nothing baring you from wearing armor, rings, trinkets, or other such equipment, but they certainly don't have the body type to be wearing chainmail crafted for a half-orc. Ultimately, it would probably be under your DM's discretion, but I see no harm in it (as the kitsune is already limited to not having weapons and needing to subsume magical impliments and such to his star ball).
On a note of Beastskin Armor, it wouldn't work for a kitsune. Not only is it a +2 enhancement cost, but Beastskin is specifically stated ONLY to work in Wildshape form, and ONLY if an additional use of the ability is expended to do so. Since a kitsune (unless its a druid) lacks both, the armor would be useless to him. However, if your DM is less inclined to allow your armor to naturally change to accommodate your form because of the 'magical' effects of Alternate Form/Self, he may be more inclined to allow you to fudge this enhancement to work for your true form.
Of course, you could also just keep two armors. One armor crafted for your true fox form, which melds into your form if you shift into a humanoid shape, and another which works in humanoid form and melds into your shape when you return to your true state...
