Hi, Pete
I can't help you out much on the actual recording (I just use my camcorder) other than agree with Cameron that recording inside your walk in closet will work pretty good.
It may even sound too dead sterile. I dunno. Your call.
Just... please don't try it in a basically empty, normally furnished room.
Everyone will tell you here no matter whatever kind of microphone you use it'll sound like echoy sh!te.
However, once you've recorded your voice over dialog a few times to work out the kinks of what looks good on paper vs. what comes out of our mouths, and you'll get a better feel for timing, and some breath control, then you can clean it up and monkey with it in post using an audio editor and a voice morpher.
http://free-audio-editor.com/index.htm
http://download.cnet.com/AV-MP3-Player-Morpher/3000-2140_4-10201978.html
With the audio editor I select and delete all sorts of amateur breath inhalations, tongue clicks, spit smacking, and general flubs.
You see, one of the great benefits of doing voice overs vs. live action is that you can screw it up six ways to Sunday and still delete the flub ups easy as pi.
With all the trash deleted I can then go back and add or subtract fractions of seconds to improve timing/delivery.
Hear a little static or tinny sound? Fine. Try a few filters and see if one knocks out what you don't wanna hear.
Yeah, you'll lose some "crispness" , but it'll be less annoying than that... whatever it was.
Okay, now that that's done and saved, pull it up in the morpher and tinker with the tone over there.
The morpher does a fair job of dropping the pitch down, but not so good at raising it.
I can make my voice sound like a trucker, but not the hooker with a heart of gold.
And you can't record Daffy Duck and make him sound like James Earl Jones, either.
You're still going to sound like a shade of yourself.
GL.
Have fun.
Don't poke yerr eye out!
Ray