First of all, consider the Linux HCL, found on this site in the Main Menu, to your right and up
I don't know how much is benefited by using a 64 bit processors if you only use it for word processing and office stuff. However the times are changing and you will soon need a processor like this for common use, so it could be useful to have in a couple of years. If you are buying now and money is not the first issue, go for it. Review the HCL(hardware compatibility list) to see what hardware linux can handle and make it work for you.
Good luck!