Here is the rumors about this car from ALLPAR.COM
From “oh20:” “Late next summer the last 2006 Viper will roll off the lines. When the employees return to work the following January, a little over 14 months from now, they will be building the refreshed 2008 "ZB" models. The 2007 model year is going to be skipped.”
From a source who would probably prefer to remain nameless: “The 2008 Dodge Viper is solid - much faster and sleeker, while still keeping the twin hump in top (on coupe models) but with a whole new front end that’s sharper and more menacing.”
Given the recent showing of a McLaren Viper, and rumors about the current V10 being “made over” by an external firm, it seems almost certain that the 2008 Dodge Viper will use a McLaren-massaged V10 engine, probably the one shown at SEMA in the ASC Diamondback Viper. That engine was rated at 615 hp, a fat 110 hp more than the current version; that Viper could do 0-60 in 3.5 seconds, a few tenths better than the current model in a genre where a few tenths are a big difference. The ASC model cut weight using expensive carbon fiber, but then, McLaren might not have been showing all their engine could do; we’ve been told to expect 700 hp but we suspect 650 is more realistic, and, indeed, we have been told by a reliable source that 600-650 hp is what we should really expect. Keep in mind, though, that the Viper V-10 is not a typical "peaky" engine and that it has tire-melting power right off idle.
Other rumors were not particularly credible - using the Mercedes V12 (not Viper-like), a V10 Hemi (expensive to create, poor emissions), a turbocharged V10 (not desired by current owners), and an even bigger Hemi V8 (again, not Viper-like). The current Viper engine, based on the LA V8 family introduced decades ago, most likely has untapped potential which could be awakened by expert tuners.
A Chrysler version of the Viper is almost certainly in the works. The Firepower may be a look at what's to come - it's a Hemi-powered, Viper-chassis Chrysler that would be cheaper to make, and would add to the volume of the Viper chassis, helping to spur profitability. By using a standard-production drivetrain, it's no doubt much cheaper to make - and performance is still respectable with a Corvette-like 0-60 in 4.5 seconds. (Keep in mind it's an automatic.) The Firepower is said to have definitely been approved.
oh20’s 2008 Dodge Viper rumor roundup summary

redicted debut: 6:30pm-8:30pm Monday September 25th, 2006, VOI9 Las Vegas
Start of production (Job 1): January 8th, 2007
End of production: July 2008 (for the 2008 model)
Series: ZB
Models: SRT10 coupe and SRT convertible (+ Special edition models)
New features:
Exterior refresh
8.4L SFI V10 engine replaces 8.3L V10 (600-650 hp estimate)
High performance alternator
New SRT-10 satin silver badging
+?
Key carryover features from 2006:
6-speed T56 manual transmission (revised?)
3.07 axle ratio
12-inch clutch
18.5-gallon fuel tank
18x10 and 19x13 wheels
275/35ZR18 and 345/30ZR19 Michelin tires
310-watt amp w/7 speakers and subwoofer
Anti-lock 4-Wheel-disc brakes
Dual side exhaust
HID headlamps
Keyless Entry
Leather wrapped Steering Wheel
Power adjustable pedals
Power windows (1-touch up)
Preferred suede seats w/leather trim
Radio RBQ AM/FM radio w/in-dash 6-disc CD
Sirius satellite radio
Sport Suspension
Tilt steering column
Colors: Viper...black, blue, red, yellow, slate crystal?, more?