We bought a new HP laptop for Dahlia in SF last June. When we bought it, there was Windows Vista in the 64bit version installed on it. So when we came home to Berlin I updated the operating system with Windows 7 in a 64bit version – Dahlia was very thankful for that because everything was running faster 
Unfortunately, problems with the new laptop started to arise over the next few weeks: There were non-working drivers, non-working apps and among many other things the standby mode was also not working. Troubleshooting these problems always pointed to problems regarding the 64bit version of the operating system Windows because most of the applications run in a 32bit compatibility mode…
…so we decided to re-install the laptop with the 32bit version of Windows 7 in February and since then, all the problems became history
There was still the question as to why one should use a 64bit version? To answer that question, please read the nicely written article on the newsweek blog: http://blog.newsweek.com/blogs/techtonicshifts/archive/2009/09/16/64-bit-computing-the-next-big-confusing-thing.aspx
To answer the question whether you should use a 32bit or 64bit version of Microsoft Office, here is a very good blog article: http://blogs.technet.com/dmelanchthon/archive/2010/04/23/welche-office-2010-version-soll-ich-nehmen-32-bit-oder-64-bit.aspx
If you unable to read German, here is the summary in English: Don’t use the 64bit version of MS Office unless you need to create or open office documents bigger than 2GB 
