It's the solar moonroof that really gets people going when they talk about the 2010 Toyota Prius.

Never mind that it only generates enough electricity to run a ventilation fan (59 Watts, or just 1/500th of what the battery pack puts out). It's still the coolest item in a long list of available options offered for the first time on the latest, brand-new 2010 Prius.

But there's a catch. You can order the Solar Roof Package, but then you won't be able to get the Advanced Technology Package. You can't have both on the same car, and that caused some grumbling at the invitation-only Prius Connection New York event we attended in February.

So to help you navigate through the thicket of equipment levels, options, and packages, here's our rundown.

EQUIPMENT LEVELS

There are four basic equipment levels--confusingly labeled II, III, IV, and V, rather than the previous 2009 Toyota Prius convention of Standard, Base, and Touring levels. Toyota executives also mentioned a fifth level that will come a little later; we surmise that may be the missing level I. Perhaps it will be a stripped-down spec for eco-sensitive but cash-conscious government fleets?

Prius II (Model 1223): This is the base model of the 2010 Toyota Prius. Standard equipment includes SmartKey keyless entry, cruise control, multi-information display, and Touch Tracer steering wheel controls.

Prius III (Model 1225): This adds (to Level II) a JBL AM/FM/CD changer with integrated satellite radio; 8 speakers; and hands-free Bluetooth mobile phone integration

Prius IV (Model 1227): This adds (to Level III) leather interior trim; heated front seats with power lumbar support for the driver; water-repellant glass; PlasmaCluster ion generator in driver's vent to reduce odors, germs, and mold; automatically dimming mirror; three-door SmartKey system; and a handful of trim and lighting upgrades.

Prius V (Model 1229): This adds (to Level IV) the 17-inch alloy wheels, plus LED headlamps and foglamps

AVAILABLE PACKAGES

Navigation Package (available on Prius III, IV, and V): A touch-screen DVD navigation system with voice activation, including XM NavTraffic and BlueTooth music streaming, plus backup camera, and SafetyConnect system with automatic collision notification, stolen vehicle location, and emergency assistance call center

Solar Roof Package (available on Prius III and IV): Includes all equipment in Navigation Package, plus solar-powered cabin ventilation system, including remotely activated air-conditioning (from SmartKey)

Advanced Technology Package (available on Prius V only): Includes all equipment in Navigation Package, plus Dynamic Radar Cruise Control, Lane Keep Assist, Intelligent Park Assist, and Pre-Collision System including seatbelt pre-tensioner and brake assist

In other words, the Solar Roof and the Advanced Technology packages are mutually exclusive. Why? Toyota executives told us that the combined weight of all those options put together would have put that specific 2010 Prius model into a different regulatory weight category.

Hmmmmmm.

2010 Toyota Prius two-tone leather interior

2010 Toyota Prius two-tone leather interior