First you have to install the wonderful pywin32 module.
It provides COM support. You need to run the makepy utility. It is located at C:\...\Python26\Lib\site-packages\win32com\client. On Vista, it must be ran with admin rights.
This utility will show all available COM objects. You can find yours and it will generate a python wrapper for this object.
The wrapper is a python module generated in the C:\...\Python26\Lib\site-packages\win32com\gen_py folder. The module contains the interface of the COM objects. The name of the file is the COM unique id. If you have many files, it is sometimes difficult to find the right one.
After that you just have to call the right interface. It is magical 🙂
A short example with excel
import win32com.client
xlApp = win32com.client.Dispatch("Excel.Application")
xlApp.Visible=1
workBook = xlApp.Workbooks.Open(r"C:\MyTest.xls")
print str(workBook.ActiveSheet.Cells(i,1))
workBook.ActiveSheet.Cells(1, 1).Value = "hello"
workBook.Close(SaveChanges=0)
xlApp.Quit()