Hi Gareth,
I did something similar whilst waiting for my toys to arrive too
If you haven't come across it before, "stacking" is a really cool technique that lets you shoot at much higher ISOs than would be otherwise possible.
Here's a quick example that I did... I found that I could just begin to see the Eta Carina nebula in my photos at ISO 6400 x 1 sec (any longer resulted in star trails), but it was very low contrast and noisy - basically a useless image.
I took a sequence of 17 consecutive shots and ran it through Deep Sky Stacker (freely available online) which removed the noise and made the nebula more visible (after levels adjustment / histogram stretching).
Oh, and one other thing... if you happen to take exposures around 1/4 sec to 2 seconds in duration, it's worth using the Mirror Lock Up feature (it's in the camera manual). Here's a pathologically bad example with a heavy lens. Shorter/longer exposures than this usually aren't affected.
Have fun!
Dave