You may be interested to know that Microsoft have now made it official that the next version of SharePoint will be released on 64 bit only. So if you have the choice today and you think that upgrading may be something you would do in the lifespam of that server then you may want to test 64 bit now. The Devil is in the detail but look to step 5 http://blogs.msdn.com/joelo/archive/2007/12/17/12-things-to-do-over-the-holidays.aspx
Steve Smith