I know that it's tacky to reply to your own post, but I
was able to get a great answer to this from Fergus Coon in
the VB.NET newsgroup, and I thought that I'd post it for
anyone that was looking for an answer:

Imports System.Runtime.InteropServices

Public Module ExcelUtils
Public Const xlCsv As Integer = 6
Public Const xlNormal As Integer = -4143
Public Const xlXls As Integer = -4143 'Alias
for xlNormal

Public Sub ConvertFile (sSrcFilePath As String, _
sDestFilePath As String, xlOutputFormat As
Integer)
Dim oExcel As Excel.Application
Dim oWorkSheet As Worksheet

Try
oExcel = New Excel.Application
oExcel.Visible = True 'Optional but good
for debugging.

oExcel.Workbooks.Open (sSrcFilePath)
oWorksheet = DirectCast
(oExcel.ActiveSheet, Excel.Worksheet)
oWorksheet.SaveAs (sDestFilePath,
xlOutputFormat)

Catch
Dim Up As New Exception ("Bad file -
Uuurghh")
Throw Up

Finally
If oWorksheet Is Nothing = False Then
Marshal.ReleaseComObject (oWorksheet)
End If
If oExcel Is Nothing = False Then
oExcel.Quit
Marshal.ReleaseComObject (oExcel)
End If
End Try

End Sub
End Module


P.S Have to add MSOffice references for this to work.