Thanks a lot for your advice, Sam. I did as you suggested and in revisiting Omega Centauri, collected several 6 minute exposures and stacked them. I tried DeepSkyStacker but unfortunately it kept generating an error message "Out Of Memory" -- it appears to have a 512Mb limit either in it's working set or on the generated output, so I went ahead and stacked them in Maxim instead.
I was pleasantly surprised to see a couple of galaxies in the resulting image, including a fairly prominent elliptical in the top left corner.
Full-sized version is available here:
http://s596.photobucket.com/user/Tau...tauri.png.html
Being one of my favourites in the night sky I am looking forward to seeing how far I can go with this target. Thanks again for your help, Sam.
Cheers,
Brett