On the whole you just open in the later version and Access will convert.
However, if you have VBA code then Access 2000 may try to interpret your code using the ADODB library instead of the DAO library. This causes code to crash because both libraries have things like recordsets but the syntax is different. To avoid this you need to open a module and go to Tools, References. Tick the DAO library and move it above the ADODB reference.
There may be issues with Access security. However, I always use my backend database to provide security so I cannot comment.