One way
(al code in a normal module)
Function SheetExists(SName As String, _
Optional ByVal WB As Workbook) As Boolean
'Chip Pearson
On Error Resume Next
If WB Is Nothing Then Set WB = ThisWorkbook
SheetExists = CBool(Len(WB.Sheets(SName).Name))
End Function
Use it like this for example
Sub Sheet_Test()
Dim SName As String
If SheetExists("test") = False Then
ActiveSheet.Name = "test"
Else
MsgBox "sorry the sheet exist"
End If
End Sub