Q:

Can i browse the files on an external mac as an external HD? 

Ive got data on an old iMac G4.  My plan was to remove the HD, put the HD in an enclosure and transfer the data from the HD.  
I looked up the iFixit guide for the process and it seems the HD isn't easily accessible.  
Is there another way i could connect to the iMac G4 (not sure what OSX version) from my mid 2012 macbook pro running 10.11.6 and browse the iMac G4's drive, without having to boot the iMac G4 ? 

A:

There is no way to access the data on the iMac G4's internal drive without power.  If you can boot the iMac into Target Disk mode (by holding down the T key at startup) then you can connect it to your MBP using the appropriate Firewire cable which will then let you access the drive as an external.