Remou had it right. Here is a RegexContains function so you can use it with all sorts of patterns, not just the one you need now.
Function RegexContains(ByVal find_in As String, _
ByVal find_what As String, _
Optional IgnoreCase As Boolean = False) As Boolean
Dim RE As Object
Set RE = CreateObject("vbscript.regexp")
RE.Pattern = find_what
RE.IgnoreCase = IgnoreCase
RE.Global = True
RegexContains = RE.Test(find_in)
End Function
Following the example from Remou, assuming the cell is A1, you'd write:
=RegexContains(A1, "^\d{1,2}$")