Restrict Characters users in Custom User Fields
 

I'm curious as to how difficult it is to restrict certain characters in custom users profile fields.

I need something that would result in the following:

First Name - must be at least two letters - no numbers allowed
Last Name - must be at least two letters - no numbers allowed.
Style of Fishing You enjoy - must be at least two letters - no numbers allowed.
Where you live - must be at least two letters - no numbers allowed.
Your Occupation - must be at least two letters - no numbers allowed.

So, as you can see I want to restrict numbers from being used at all, and also want to require a two character min. on the required user fields.

Any help on this would be greatly appreciated.