Browsing the net, I came across this link: http://www.opencircuits.com/Techniques, which contains a really nice and cear illustration how to handle separate analog/digital ground planes on a PCB.
There's a lot of other nice tips too, and don't forget to follow the links to the external docs, especially the Powerpoint presentation from Mississippi State Uni.
There's a LOT of great stuff for PCB design here.
And when you're done with that, step back up in the Wiki-hierachy and find tons of information about components, footprints e.t.c.
If you think you already know all this, do help improve on the site by supplying YOUR knowledge to this great resource.