It seems like a fantastic idea to draw each slide by hand - you may even end up with a powerpoint presentation that is original and won't turn your audience off before you start...
It is easy to get your pictures into a presentation, there is a "photo album" option on the insert tab (it is available on older versions too but you need to be careful according to this.
So the problem is just one of getting your drawings into the computer as picture files. A cheap flatbed scanner is just a pain when scanning more than a couple of documents, but you may be more patient than me. You could get yourself a scanner with a feed mechanism, but these tend to be expensive compared to flatbed scanners. If you are not doing too many slides then there still exists at least one manual feed scanner, having no lid will make it less of a pain than a normal flatbed scanner.
Or you could get yourself a graphics tablet and draw straight into the computer.