IsAlpha Function:

The IsAlpha function checks a string and allows only white space, letters of the alphabet, or underscore characters to pass as valid input.

boolean = IsAlpha(string)
Example Usage:
 ' IsAlpha returns True
response.write IsAlpha("This Thing")
response.write IsAlpha("This_Thing")
response.write IsAlpha("Some_Other Thing")

 ' IsAlpha returns False
response.write IsAlpha(37.8)
response.write IsAlpha("37.8A")
response.write IsAlpha("ABSD= acscrrrw!")
ASP Source Code:
Private Function IsAlpha(byVal string)
	dim regExp, match, i, spec
	For i = 1 to Len( string )
		spec = Mid(string, i, 1)
		Set regExp = New RegExp
		regExp.Global = True
		regExp.IgnoreCase = True
		regExp.Pattern = "[A-Z]|[a-z]|\s|[_]"
		set match = regExp.Execute(spec)
		If match.count = 0 then
			IsAlpha = False
			Exit Function
		End If
		Set regExp = Nothing
	IsAlpha = True
End Function