/^(?=.*[a-z])\w+$/i

[download]
(translation: all word characters, but at least a letter)

You don't say if you think underscores are acceptable... 

/^(?=.*[a-z])(?!.*_)\w+$/i

[download]
(translation: All word characters, but at least a letter, an no underscore)

There.

In reply to Re: Simple regex question by bart
in thread Simple regex question by zuma53

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