Focussing on a bright star such as Sirius should get you going. Alternately, you can try focussing on a distant object during the daytime.
Note that you may have some problems bringing the CCD camera into focus if there is insufficient inwards travel on your eyepiece focusser. If this is the case, then you can see Mike Selway's excellent guide:
Modifying a Newtonian Tube for DSLR Photography
Hope this helps.