I read about images captured and rendered with descriptions such as "400 images stacked" what does this mean? I thought when you took a picture a shutter opend and closed and captured an image and then you developed it.

What is stacking and how does it work ?

I'm going to be taking pictures with my Dob. using a t-adapter and t ring and an SLR. Does this stacking have anything to do with film photography or is it strickly a digital method?

Maybe a quick astrophotography 101 course is in order here?

stacking is strictly a digital imaging technique where multiple images are combined to increase the signal:noise ratio.  it effectivly reduces noise, the digital equalavent to film grain.  noise is a random effect so combining images reduces noise while maintaining the non-random signal.

if you haven't already done a search for film astrophotography you might try thid link:

http://www.petesastrophotography.com/

i'm sure there are many more

best of luck!

Here is an overview of the different methods of astro imaging that you can read and should help. 
http://cs.astronomy.com/asycs/forums/t/19319.aspx

I can tell you this from experience taking images through a 10" Dob.  Good Luck! It takes lots of trial and Error. And with a Dob and an SLR you can't achieve focus. Most stock focusers are to high.

You would probably be better off attempting some Afocal images of the moon and planet. Without tracking that is all you are going to be able to shoot through your Dob anyways. Unless of course you have some kind of eq tracking platform for it.. For DSO's you need the ability to track, and to track accurately for long periods of time. Even stacking multiple shots with a Digital SLR will show tracking errors. And I can also tell you that you don't even want to attempt to track by hand when taking any kind of image through a Dob, unless you want smeared images. 
Also trying to attempt this with a 35mm SLR might just prove to be futile. There is no way to tell if you got the shot or got the correct exposure untill you can have the film developed. It is extremely easy to overexpose the moon and planets with any kind of camera..  You might think about getting a nice WebCam such as the Phillips SPC900NC(ToUcam Pro III) that you can get from Wal Mart for under $80.00 then for about another $20.00 get the Mogg adapter so you can fit it to the 1.25" focuser. This will get you a much nicer image, with a higher magnification. And can be done much easier with a DOB..  

Afocal through a Dob is a good start for getting your feet wet, however, it is still tougher than it sounds and can and will cause a lot of frustrating moments. For every one shot I kept taken with a Point and Shoot Digital camera which was somewhat presentable, I probably took more than 100 that I scrapped to the trash. Every attempt I made with a 35mm SLR was over-exposed or under-exposed.   Film is tough even in a telescope that does have tracking.. You will waist a lot more money on film and devloping than you will get images worth keeping..  

Not trying to discourage you, just trying to make you aware of what you're in for when you get into astrophotography..  Film imaging is tough, however it is a great way to gain experience. Even though you cannot stack individual pictures like you can with digital images, you can still learn a lot about post processing of the images.  Post processing is vitally important to good images.. Something I've been trying to learn for a few years now..

 Good Luck, and hope all the info we are providing you helps. At the bottom of that page I linked you to is some more links that will answer a lot more question than I could ever think of answering for you.. Check them out after reading through my post. And the Link provided to you in the previous reply is a great place for learning about film astrophotography..

Have A Nice __________