Only if you have anyone going to need to use them from Access 2003.
Also, you don't necessarily need to change them from 2003 to 2007 files. Only if you want to take advantage of some of the newer features will you need to do that. The 2003 files can work just fine in 2007 (some changes may need to be done, but more likely than not they won't have to be). If you are using Access' built in security then you can't move them to 2007 as 2007 does not have User Level Security in the accdb file format.
Hope that helps.