Malcolm, congratulations on your Horsehead image. Many of us started out with un-modded DSLRs (450D in my case).
I encourage you to consider a filter mod for your camera, to open it up to more Ha. The 450D is easy to work on, and the process for the filter mod is very clearly set out by Gary Honis on his website.
http://dslrmodifications.com/rebelmod450d1.html
Have fun.
Glen