This probably isn't the best website for your question. I'd check out hometheaterspot.com. Lots of knowledgeable folks there on all things tv/projector/HT etc.
Pick a Home Theater projection screen. Don't worry about slide projector screens, because you can use any home theater screen for a slide projector, since the quality of the slide images isn't critical.
Check this site for more information on how to select a projector screen: http://www.da-lite.com/education/
If you wanted to go-cheap;go to Home Depot and pick up a white/room-darkening window shade. The 'room darkening' is better than the 'light filtering' Roll up feature./ pick your size;mount it on the wall.For about 35bucks;you'll be amazed.I used one for a time. See and you thought all the rocket scientists were at another forum.
Screen's cost a lot of money, I would get the projector first. These new projectors are nothing like the projectors of old..they output a bright enough picture that you can enjoy them even on a wall in you home with the lights turned off. I used mine on a flat white wall for two months while I did research on the type and cost of screen I would need. Avguygeorge's idea is another good way to enjoy your projector untill you have made up your mind on what you need.
Screens come in all shapes and sizes, they also come with different amounts of GAIN. GAIN is the amount of help that the screen (they come in different colors and finish) will offer a projector with a lower light output or in a room that is not controled of all outside light. In other words, the screen you need for your projector and your room would (could) be different than what I need. You may even need..no gain.
Screen shape and size is another matter that should cause you to take a wait and see out-look. I would have bought a screen that was to large had I not had a couple of months to play around first. I am going to give you a couple of links to some screen info to read up on, I'll have to post another response though because I don't feel like re-typing this.
The first link has screen buyer guide and the second link will show you how many different size screens are out there but is still not a full picture because there are also many other types and shapes. I would also use the search feature at the avsforum.
The best home theater screen size for you will vary WILDLY (perhaps by a factor of 2) based on personal taste, source material, aspect ratio, your sensitivity to source artifacts, what projector you use, and how you feel about it's artifacts.
You really need to buy your video projector, live with it for a while, and see what works for you.
With CRT projection I sit 11' from an 87x49" screen for most sources and move up to 9' for nice scope transfers. I'd need either a much smaller screen or longer seating distance with the last LCD projector I demoed.
Once you have the projector you can start worrying about screens. Stewart makes very nice screens, and if you're looking at nice shadow-boxed, wide, velour coated frame the price premium may not be interesting ($210 for my screen compared to the same specs from Dalite). Carada is much less expensive. A white painted piece of MDO, wood frame, and velvet to soak up overspill is almost free.