[jQuery] Only number

Hello,
i'm working in a automatic validation for forms. Ok, but the problem
is how can i allow only numbers in a input?
or, numbers and "."? or only alpha caracters, you know?
i need allow and deny what i want!
i found a plugin, called jQuery AlphaNumeric, but it doesn't allow
"delete", ctrl + v or arrows.
Please, help me!
sorry my english!
thanks!
Lourenço