Here's a way to crack the zip files with passwords. First of all download and install fcrackzip, if you're on a debian based distro the command to run is :

# aptitude install fcrackzip

That's all. Once it's installed you'll have to run the command with few parameters here's some explanation of some options :

-b option will let you select the brute force attack mode. This means that it'll trie all the possibilities.

-c option will let you select the characters to use for example if you set it to a this means that it'll only try with lower case alphabets.

possible values are :

a   include all lowercase characters [a-z]

A   include all uppercase characters [A-Z]

1   include the digits [0-9]

!   include [!:$%&/()=?{[]}+*~#]

-v option make it more verbose.

for more details about that you can use man :

$ man fcrackzip

Example of use :

$ fcrackzip -b -v -c aA1 file.zip

This will try to find the password by using a brute force attack method and by trying lower and upper case alphabets and numbers.