Did Word 2000 perhaps come as part of Works 6? In any case it sounds like the Works 8 CD is not an upgrade CD, so you'd better uninstall the old stuff. Just one word of warning: I think Works 8 comes with Works wordprocessor, which doesn't have all the features of Word. To get Word itself you need Works Suite. (I only discovered this after paying extra for Works 8 with a new PC & I was pretty annoyed. Mind you Works wordprocessor has all the essentials.)
If you really need a top-notch package including a top wordprocessor, just download OpenOfice click here - its free and its as good as Microsoft. Just remeber to change the default wordprocessor format to Word XP (rather than the OpenOffice format) if you want to open your docs on other computers.