When hanging door & window casing, I typically use both an air nailer as well as hand nails. WHen attaching oak casing, I usually hand nail the outside corners of my 45 Miters to "tighten" the joints. Trying to predrill these with my 14.4v cordless drill can be quite a task. Usually I end up scarring the finished drywall while drilling. Can anyone offer a suggestion here on how to avoid this? I was thinking of getting a smaller cordless for just this task, possibly a right-angled drill.

If you are already willing to spend a little money to get the job done your best bet would probably be to buy an 18 guage brad nailer and shoot 1" brads to hold the miter tight...it is the quickest and neatest way i've found to do it...plus you can get a good brad nailer for about $80 @ home depot or similar store