There are several differences to consider when deciding whether to purchase the D5100 or D7000. They both share some of the same features, but the D5100 is just a step before the semi-pro D7000.
First the differences:
They both have:
http://nikonites.com/d5100/2498-d5100-vs-d5000.html
http://nikonites.com/d5100/2499-d5100-vs-d3100.html
http://nikonites.com/d5100/2507-d5100-vs-d90.html
http://nikonites.com/d3200/5672-nikon-d3200-vs-d5100.html
http://nikonites.com/d5200/9382-d5200-vs-d5100.html
First the differences:
They both have:
- The same 16.2mp CMOS sensor
- 100-6400 ISO - Expandable 12,800, 25,600
- Video full time auto-focus
- Live view shooting
- Microphone jack
- The same 3.0in monitor (D5100 swivels)
- Plastic bodies
- SDXC card compatibility
http://nikonites.com/d5100/2498-d5100-vs-d5000.html
http://nikonites.com/d5100/2499-d5100-vs-d3100.html
http://nikonites.com/d5100/2507-d5100-vs-d90.html
http://nikonites.com/d3200/5672-nikon-d3200-vs-d5100.html
http://nikonites.com/d5200/9382-d5200-vs-d5100.html