As the system is used much more frequently, the files become fragmented and a possibility of corruption. This explains why the system started becoming slower after installing MS Office software.
You should be able to speed up your systm with the following steps:
1) Run Scandisk from [Programs]->[Accessories]->[System Tools], then run [Disk Defragmenter] from the same menu.
2) Also check for orphaned files in the "C:\windows\temp" folder (it should be empty when Windows is restarted.)
3) Unload uneccessary application at start-up, click [Start]->[Run], type "msconfig" and press [OK].
4) In [General], select [Selective StartUp] and uncheck [Process Config.sys] and [Process Autoexec.bat].
5) Uncheck [Load Startup group items], and click [OK].
Please note that the above mentioned points are a guide for the maintenance of the system software. We would recommend some housekeeping be performed on the software installed, i.e. remove/uninstall any unneccesary software so as to free up more disk space and speed up the system.