Do you mean the I-Ride trolley? If so, it's still a fair walk from the nearest stop to Universal (probably 20-30 minutes)
http://www.iridetrolley.com/pdf/service.pdf
You could switch off to the green line trolley but it's a bit of a faff.
The
cheapest way to get to I-Drive from Pop is to catch the Lynx bus (number 50 I think) from the Ticket and Transportation Centre to Sea World, then you can hop on the i-ride there.
I-Ride Map
This is how you would need to do it:
Catch a bus from Pop to Magic Kingdom
Walk or get the monorail to the Ticket and Transportation Centre
Catch the Lynx bus to Sea World
Catch the I-Ride to the nearest stop to Universal
Walk to Universal
The whole journey would most likely take about 2 hours.
Then you have to do the whole lot in reverse to get back.
Would be much easier and quicker (and not that much more expensive) to get a taxi or Mears transportation (in my opinion).