There's a bit of code
here. Here's
one on the newsgroup.
The short answer is this (which came from
here)
$a = New-Object -comobject Excel.Application
$a.Visible = $True
$b = $a.Workbooks.Add()
$c = $b.Worksheets.Item(1)
$c.Cells.Item(1,1) = "A Value in cell A1."