Are you connecting to an SQL2000 database in ssms 2008 or trying to open SQL2000 DTS packages that where deployed to SQL2008 R2?

If its the former then I would suggest setting up a VM machine with SQL 2000 Enterprise manager installed and using that to manage them.

If its the later then I would strongly suggest redeveloping them in SSIS 2008 as this is a depricated feature in 2008r2 and they have very limited support, see http://msdn.microsoft.com/en-us/library/bb500440(v=sql.105).aspx

Also it will be better to redevelop them in SSIS 2008 as SQL 2012 no longer supports these types of packages, see http://technet.microsoft.com/en-us/library/bb500429.aspx