All possible combinations of a combinations of characters

I need to get every possible combination of characters that follows a r开发者_开发技巧ule.

Say:

Length: 5-6

Characters: ABCabc123

I should get stuff back like this:

AAAAA
AAAAB
AAABA
AAABB
..
..
AcbC13

Is there any way to do this quick an efficiently?

Please keep in mind I am using VB.net but I do understand concepts related to just general speaking.

There is some good code to do exactly that here: http://www.codeproject.com/KB/recipes/Combinatorics.aspx