Jungle's got it right. The support is the 2002/2003 lows. Once the Dow broke 10,000 that became the only technical support level. So look for something around 7500 to 8000 as the near term low. It could happen as early as tomorrow. Then it's quite possible there will be a rally off that low of 5 to 10%. If that's followed by a re-test of the low ( a W shaped bottom on the chart ) then a base may have been built. It's hard to say now though with so much government intervention in the markets and nationalization of financial institutions.
My bet is that we'll be in a bear market for at least 3 years and possibly much longer. Most people seem to use the logic of the post 1982 era as their foundation for making statements about buying on the dip and dollar cost averaging. Use that logic for the 1967 to 1982 time frame and all you would have done is lose money to inflation as the value of your portfolio stagnated.
If you are young a long term sideways market isn't the end of the world. It would give you the opportunity to buy for many years at roughly the same price. When the market does turn up again you'd have a very good base to start from.
With the amount of negative sentiment in the market as indicated by S&P put options a "bear squeeze" could make for an even larger move up. The trick is timing it right. That means buying near the bottom and then selling near the top because it will inevitably fall again based on economic fundmentals and the ongoing financial turmoil.
That's my two cents.
Typhoonpilot
P.S. Gold did really well in the last big bear market, making it's high very near the end of that bear market. Have at least 5% of your portolio in gold.