The i-net+ is essentially a certification for non-technical people to learn the basics of how the internet/networking works. AKA people with business degrees looking to get a leg up on their resume.
The Net+ is more an intro to actual networking technologies and is oriented for people intending to actually advance in a technical field.
There's probably a decent amount of overlap between them since the entry level stuff is all the same technologically (DHCP, what a router does, what a switch does, etc), it's more the way they are presented.
If you were going to a technical school for IT, I have no idea why they wouldn't just focus on the Net+ instead, I guess it depends on what program you were enrolled in though. Either way, they're both very basic certs. As far as I know they do not even administer the i-net exam anymore.