U.S. stocks slipped on Friday, after the Dow's eight days of gains, as a rising dollar hurt crude oil prices and weighed on energy stocks.

Renewed worries about Greece's debt problems sent the euro to more than a two-week low against the greenback. The stronger dollar, in turn, hit the price of dollar-denominated commodities such as oil and gold because it makes them more expensive for holders of other currencies. That effect spilled over to energy stocks, with the S&P Energy Index <.GSPE> down 1.4 percent as U.S. crude oil futures <.CLc1> lost 2.5 percent to $80.18 a barrel. Earlier, spot gold fell more than 1 percent to a session low.

A looming congressional vote to overhaul the U.S. healthcare system will keep health-sector stocks in focus, with Aetna Inc up 4.3 percent at $34.66 after it forecast first-quarter earnings above consensus. The Morgan Stanley Healthcare Payor index <.HMO> gained 2.7 percent.

That Aetna is guiding higher in the face of the legislation is obviously a positive, but the vote is concerning, and leading people to take profits in areas that have had a nice run, said Justin Wiggs, managing director at Stifel Nicolaus Capital Markets in Baltimore.

The Dow Jones industrial average <.DJI> dropped 50.79 points, or 0.47 percent, to 10,728.38. The Standard & Poor's 500 Index <.SPX> fell 6.77 points, or 0.58 percent, to 1,159.06. The Nasdaq Composite Index <.IXIC> lost 18.94 points, or 0.79 percent, to 2,372.34.

Boeing Co rose 1.4 percent to $71.84 after the Dow component said it will move up production for both its 777 and 747 widebody planes, citing increased demand.

Weighing on the Nasdaq was Palm Inc
, which tumbled 18.9 percent to $4.58 a day after it warned that quarterly revenues would be far below expectations as low demand for its smartphones left wireless carriers with excess inventory.

SunPower Corp sank 13.7 percent to $19.03 a day after it gave a weaker-than-expected profit outlook for 2010, prompting a number of analysts to cut their price targets on the stock.

Electronics retailer Best Buy climbed 2 percent to $41.25 after Goldman Sachs upgraded the stock to buy, citing prospects for a better-than-expected 2010.

Regarding Greece and its huge debt burden, the European Union's monetary affairs chief urged the bloc's leaders to agree on a standby aid package for Greece next week. But investors fear German reluctance could hinder the effort.

Volume has been thin during the week and volatility has dropped considerably. The CBOE Volatility Index <.VIX> is down roughly 5 percent this week and hit its lowest mark since May 2008.

Friday marks the second day of a convergence known as quadruple witching, when four types of options and futures contracts expire, possibly triggering volatility and higher volumes.

(Reporting by Ryan Vlastelica; Editing by Jan Paschal)