I have a 64 3000+ & a SATA drive.
Word seems to take about 4 secs to load on my pc wher at work it is instant. They use P4's on IDE drives. Admittedly they are only 20 GB wher mine is 120 GB, :)
Have u defragged the drive?
Also you could reinstall windows, then put your software on next (after your drivers etc)
Also if its part of a works package only install the components needed.
You may have a virus checker which does a scan of the documents before they open. I know my Norton does this.