Hi, Iona,
Yes, I've been to Moscow many times. What you want to see depends on your interests. The obvious one is a visit to The Kremlin and also Red Square to see St Basils and Lenin's Tomb. Thdere are also some spectacular Metro stations - the underground train as a work of art.
After that, you can usually get a lot of entertainment out of the Circus - there are at least two in Moscow. Then there's the Bolshoi Ballet. You might also take a walk around Gorky Park and also the Central Park (which has been renamed from the rather ironic "Park of Soviet Economic Achievments".
A good guide book will help more that I can, as you can pick whatever suits you. Also be sure that you read the Foreign Office's guidelines for visiting Russia and make sure you have VERY good travel insurance. Get yourself a phrase book - some Russians speak very good English and some also have some German. However, English is not as widely spoken as in western Europe.
If you want to know more, let me know. I know a Russian person very well indeed (in fact,she's my wife!) and although whe's not from Moscow, she will certainly be able to give you a bit more information that I have.