I do not have experience with either, but looking at the literature and the pictures, the Delta 66 lacks XLR inputs and 8-channel ADAT, which are deal-killers for me. The 1212M has the ADAT, but requires an external device to convert it to digital if you don't want to be restricted in your types of inputs.
And even though you might think "acoustic guitar + singer = 2 inputs" remember that you might decide to set up a pair of condensers in X-Y... and maybe you'll want a room mic. That's 4 inputs. And then a friend stops by... Yes, as word's gotten out that you can record stuff at my place, that's happened to me quite a few times. Bottom line, if you've got it, you'll find a use for it. And if you don't, a couple of your friends will.... ;-)
And that's where the 1212M really seems to start making sense. Right now, if you go on Amazon, the 1212M PCIe is available for $102 with free shipping. Use it with a Behringer ADA8000 (used on ebay for $125, or new from lots of places for $175). That's an 8 channel set up with crappy, somewhat usable but completely bypassable, pre's for $227-277. So that, plus the DMP3 you already have gives you 2 good channels, plus 6 "gotta just get it in there as best I can with lousy pre's" channels... for around $250 ($400 with the DMP3). Can't beat that! thumbsup
If there's a better value in low-end recording than an 8-channel ADA8000 ($175) feeding ADAT into a 1212M ($102) at 24/44.1, I can't fathom what it might be. Yeah, I'm sure the Behringer pre's aren't as nice as the mackie's or the Focusrites... but let's be realistic here. They all stink, it's just a matter of how bad. Sooner or later, your goal is going to be to get away from them... and with this set up, you've already got everything you need to take that step away... And your AD/DA isn't tied up with the audio interface, so you can upgrade them separately. Otherwise, you'll just be shopping again for a whole new kit down the road.
As to your questions, I really don't see how Vista could make noise on a recording except via the drivers. So make sure you're using the right ones, preferably with low latency, etc. I've been using Vista for years and have not had an issue recording on it.
I also have also used Win7 and like it a lot more. As of June 2010, the 1212M has Beta drivers for Windows 7, but check a forum (and take careful note of the dates of the posts, lest you get info which is not up to date) to be sure. I have no personal experience on this yet.