first up, you don't need DCOM on your server, if you have excel installed, that should be enough.
secondly, the manual covers a way of doing this in the user notes, so i won't go over it here...
lastly, if you open your excel spreadsheet manually, and excel gives you a dialog box of any kind, you could run into problems with excel not being closed from php.
good luck with it tho, it's pretty straight forward...