Kevin:

I've used a tablet PC for that function, but that is both expensive and requires some practice to smoothly switch between projected sources - assuming that you use a different PC for projecting other parts of the service, and the pastor doesn't want to run it all from a tablet PC.  We do have a church laptop, from which we run the normal projection, but that doesn't have digital ink capabilities.  It is rare to find a PC that has both the multimedia capabilities and the digital ink capabilities and a decent price. 

My answer is very old and decidedly low-tech.  We've used an overhead projector and transparency sheets, on which our pastor writes.  This is in contrast to our high-tech ceiling mounted projector and the PC with Sunday Plus on it.  We've used both in the same service, from time to time.  We've talked about having an artist from our community draw on overhead transparency sheets with colored transparency markers during the service, to allow people to watch an artistic representation develop while the discussion develops, but we haven't been able to arrange that yet.

Sorry I'm not more help.

Kevin,

 There are a number of different ways to accomplish what you are talking about....   If you have a tech mind, you can try using a wii remote for a multitouch digital whiteboard.....  I have seen this work pretty well, but it does take some one who is a "techie"  You can watch a youtube video of this here: http://www.youtube.com/watch?v=5s5EvhHy7eQ

Here is another option that we use are our church that is low tech...   We built a glass board and use paint markers to draw pictures, illustrations, etc... similiar to what you would see on a military sub...   Here is a picture of one of our services...  I can get you a closer and better picture if you wish...

Tim Peterson
Creative Arts Director
Crossroads Church
www.crossroadscolorado.com