One of the best ways to stop pin holes from messing up your shirts is to tape the whole screen up on the botton side around the image with 3" paper tape .. pin holes can pop up at any time .. this will prevent ink from getting on the printed work ...  also if you see small pin holes around the emage after you've burned the image you can use finger nail polish to stop up the holes in your screen  this works great .. We use Red finger nail polish because it's easler to see .. We don't reclaim our screens we just tare them out, save the frames and put new mesh in ..   One more little hint .. Try pushing the screen across the image instead of pulling it .. its less work on the fingers .. use your thumbs to push the squeeage  its a more natual feel ..   try scooping the ink taking it over the print then push the squeeage across the image the print looks way more cleaner  ..  one more hint .. White ink is very thick push your squeeage across your print twice .. Once youve printed your image on your shirt dry the print then print it again it makes the print look better on darker items .. I know a lot of people may already know this  but i was trying to help the first time people more .. I know it was hard to get help when i first started out ..

Just go to a copy shop and ask them to copy your art onto an overhead transparency. You can also print at home if you have a laser printer and the appropriate sheets.

The problem with this method is, of course, your art can only be 8 1/2 x 11. To get it bigger, you could take your art and screen to a screenprinting shop and ask them to blow it up and expose it for you. 

I'm too lazy to type up the steps myself, but this guide should explain how to create a halftone bitmap - just ignore the stuff about multiple screens.

Be aware that the halftone dots have to be fairly large, so don't expect a lot of detail to survive.