Peter,

Here is a macro to do that:

Sub MultiFindAndReplace()
'
' MultiFindAndReplace Macro
' Macro created 1/7/2003 by Gregory K. Maxey
'
Dim WordList As Document
Dim Source As Document
Dim i As Integer
Dim Find As Range
Dim Replace As Range
Set Source = ActiveDocument
' Change the path and filename in the following to suit where you have your
list of words
Set WordList = Documents.Open(FileName:="D:\My Documents\Word Documents\Find
and Replace List.doc")
Source.Activate
For i = 2 To WordList.Tables(1).Rows.Count
   Set Find = WordList.Tables(1).Cell(i, 1).Range
   Find.End = Find.End - 1
   Set Replace = WordList.Tables(1).Cell(i, 2).Range
   Replace.End = Replace.End - 1
   Selection.HomeKey Unit:=wdStory
   Selection.Find.ClearFormatting
   Selection.Find.Replacement.ClearFormatting
   With Selection.Find
       .Text = Find
       .Replacement.Text = Replace
       .Forward = True
       .Wrap = wdFindContinue
       .Format = False
       .MatchCase = False
       .MatchWholeWord = False
       .MatchWildcards = False
       .MatchSoundsLike = False
       .MatchAllWordForms = False
   End With
   Selection.Find.Execute Replace:=wdReplaceAll
Next i

End Sub

You will have to create the Word list in a two column table and save it.
You will need to identify your WordList in the macro code.