Hi Daine. That's a nice shot with your D90. They're a great camera

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I agree with Kevin regarding noise. With a bright subject like the moon you can go for a lower ISO to reduce any camera noise, the slower shutter speed required is not going to cause problems. Bracket your exposures which will give you a choice. If you do want to use high ISO, the D90 has built in noise reduction (NR) which takes a separate black frame and subtracts it, all within the camera. You see only the final picture.
Stacking of your images will give you the ability to improve the overall definition of the image. Autostakkert works pretty well and is a freebee, but if you already have Photoshop, (I have CS3) it can do the job too; just select your best images and load each frame onto a separate layer, then do an auto-align layers. Afterwards you can have a look at your levels and adjust for best effect and detail.
Its a long steep learning curve which we are all on. I get the feeling that the top is almost asymptotic.

Robert