First, this solution requires SQL Server 2005+. Second, at the bottom, I offer an alternate Split function which does not use a cursor. Third, here is a solution that does not rely on the values being of a specified length but instead that the delimiter is consistent:

Select Row_Number() Over ( Order By Z.PairNum ) As ItemNum
    , Min(Case When Z.PositionNum = 1 Then Z.Value End) As [Start]
    , Min(Case When Z.PositionNum = 2 Then Z.Value End) As [End]
    , Z.RowId As SourceRowId
From    (
        Select T2.RowId, S.Value, T2.PairNum
            , Row_Number() Over ( Partition By T2.RowId, T2.PairNum Order By S.Value ) As PositionNum
        From    (
                Select T.RowId, S.Value
                    , Row_Number() Over ( Order By S.Value ) As PairNum
                From MyTable As T
                    Cross Apply dbo.Split( T.ProductDescription, ';' ) As S
                ) As T2
            Cross Apply dbo.Split( T2.Value, '-' ) As S
        ) As Z  
Group By Z.RowId, Z.PairNum

And the Split function:

Create FUNCTION [dbo].[Split]
(   
    @DelimitedList nvarchar(max)
    , @Delimiter nvarchar(2) = ','
)
RETURNS TABLE 
AS
RETURN 
    (
    With CorrectedList As
        (
        Select Case When Left(@DelimitedList, Len(@Delimiter)) <> @Delimiter Then @Delimiter Else '' End
            + @DelimitedList
            + Case When Right(@DelimitedList, Len(@Delimiter)) <> @Delimiter Then @Delimiter Else '' End
            As List
            , Len(@Delimiter) As DelimiterLen
        )
        , Numbers As 
        (
        Select TOP (Len(@DelimitedList)) Row_Number() Over ( Order By c1.object_id ) As Value
        From sys.objects As c1
            Cross Join sys.columns As c2
        )
    Select CharIndex(@Delimiter, CL.list, N.Value) + CL.DelimiterLen As Position
        , Substring (
                    CL.List
                    , CharIndex(@Delimiter, CL.list, N.Value) + CL.DelimiterLen     
                    , CharIndex(@Delimiter, CL.list, N.Value + 1)                           
                        - ( CharIndex(@Delimiter, CL.list, N.Value) + CL.DelimiterLen ) 
                    ) As Value
    From CorrectedList As CL
        Cross Join Numbers As N
    Where N.Value < Len(CL.List)
        And Substring(CL.List, N.Value, CL.DelimiterLen) = @Delimiter
    )

SQL 2005/2008

with prods as
(
select 1 as RowID, '0296620300-0296620399;' AS ProductDescription1 union all
select 2 as RowID, '0296620400-0296620499;0296620500-0296620599;' AS ProductDescription1 union all
select 3 as RowID, '0296620600-0296620699;0296620700-0296620799;' AS ProductDescription1
) 

select 
 ROW_NUMBER() OVER(ORDER BY RowId) as NewRowID,  
 LEFT(Part,10) AS Start, /*Might need charindex if they are not always 10 characters*/
 RIGHT(Part,10) AS [End],
 RowId as SourceRowID  from prods
cross apply [dbo].[ufn_stg_SplitString] (ProductDescription1,';') p

Gives

NewRowID             Start      End        SourceRowID
-------------------- ---------- ---------- -----------
1                    0296620300 0296620399 1
2                    0296620400 0296620499 2
3                    0296620500 0296620599 2
4                    0296620600 0296620699 3
5                    0296620700 0296620799 3