Hi Mark,
You shouldn't run the PIC on 7V. The datasheet for the 18F452 says that the supply voltage should be between 4.2 and 5.5V - and that's probably the same for most other PICs too (not LF). So if the external circuit can't operate correctly on 5V (try it) you need to figure out a way to supply it with 7V. If you can fit another regulator that is probably the easiest way.

Now, for the analog inputs. Yes you need to bring the 0-7V signals down bit. If you are using Vdd as reference for the ADC you need to bring it down to 0-5V (if Vdd is 5V). A simple voltage divider will work fine. If you are using an external reference for the ADC the input obviously needs to span whatever the voltage the refrerense is set to.

Hope it helps

/Henrik Olsson.