The above link is for Acrobat Reader is for version 6 (which was quickly superceded and for good reason).
If you are running XP, go for the latest version - 7.
Version 7 isn't compatible with ME. Although version 6 will run on ME, it is a pig and very slow to load (although there is a workaround if you are interested). Personally I'd go for version 5 with ME. You'll occassionaly get a warning about the PDF using capabilities of a later version, but I've just clicked though this without problem)