This "good old" software was officially discontinued on September 30th, 2006. That means there are no updates of any kind, and no official support from Sage Software.
Business Computer Centre will do its best to support ACCPAC Plus users, but relying on this 1980's-era software to run a modern business is a little like keeping your 1975 K-car. You may be able to keep it running, but the reliability will be low, the costs will increase each year, and when it finally fails, you will have a emergency situation to deal with, usually at the worse possible moment.
However, in the interim, here is some information that may be of help.
Running ACCPAC Plus on Windows 2000. (pdf) Similar rules apply to Windows XP.
Running ACCPAC Plus on Windows ME. (pdf) If you are going to use obsolete software, you might as well try to run it on an obsolete operating system!