Diablo II is kind of a fun game and everything, but a little on the long side. But what if, after playing through the game a time or two that you just wanted to experience a certain part of the game, or wanted to try out one of the other classes without actually building it up from the ground?
Good news for you, then, there is!
First, update your copy of Diablo II to at least version 1.10. Just connect to Battle.Net and and you'll be in great shape. Then get out of you game and find your Diablo II shortcut. Right-click on it and select 'Properties'. Now modify the contents to the right of the Target field (after the quotes) so that there's a dash, the word 'act' and a number, all run together. So, if you want to start in Act 5, you'd append '-act5' after the quotes, and without the quotes.
Then start up the game and create a new character.
Enter the game and behold!
You're now at the beginning of the act you chose, your character's an an appropriate level, and you have all the skill points you need to spec your character any way you want.
What else could you ask for?