g1smd - 9:36 pm on Oct 9, 2012 (gmt 0)
Unless the new CMS was designed from the start to use the same URLs as the old CMS, changing the code to deal with that is going to be quite complicated. The new CMS would need to link to the old URLs.
It's probably better to redirect requests for old URLs over to the new URLs. There's short term indexing and ranking issues, but if the new CMS is well designed there will be long term benefits.