DCTP Forums

I'm not entirely sure what you mean by episodes, but I will try to help.

If by episodes, you mean chapters, there is a list at http://en.wikipedia.org/wiki/Case_Closed .
There's a list of episodes in http://www.geocities.com/miyanosama/ .
Here's another helpful site: http://forums.dctp.ws/viewtopic.php?t=3.0

Generally, there's around 9-11 chapters to a volume.
As for the other stuff you wanted, what language do you want? The front cover varies slightly from the Japanese version to the English version.

If by episodes you mean chapters, it's as Blackcat says, it's usually 9-11 chapters per volume. If you mean anime episodes, usually 3-4 chapters are made into a 1-episode anime. There's a complete list at dctp.ws, look at the left sidebar and click at "DC chapter list", pictures of the front covers of the Japanese version are also there.
The back covers of the volumes have keyhole views of the characters, one character per volume. They can be viewed here.

Conan324 wrote: thanks for the help...but in one of the keyholes there was ran naked, does this keyhole also appear in the eng. version?

The volume 2 keyhole is the same in the Case Closed adaptation.