Recent polls in the race for the Democratic nomination for President show Obama strongly leading in Vermont and leading in Texas (also here), while Clinton leads in Ohio (also here), and strongly leads in Rhode Island. Clinton's margin of support over Obama in Ohio has declined, however, which reduces the likely gain in net delegates that she can expect to secure in the state. Primaries or caucuses (or both) will be held in each state on March 4.
[UPDATE: It looks increasingly likely that Obama and Clinton will capture equal numbers of delegates on March 4 from the four races combined.]
Clinton needs strong showings in Ohio, Texas and Pennsylvania to make up a current deficit in delegates (both total and pledged). Bill Clinton has said publicly that Hillary Clinton needs to win both Ohio and Texas to remain viable in the race for the Democratic Presidential nomination.
A CBS national poll, in line with most (although not all) recent state and national polls, shows Obama doing much better in a head to head race with McCain than Clinton does. States Obama seems likely to win v. McCain that Clinton does not include: Oregon, Nevada, Colorado, Iowa, Wisconsin and Virginia. Clinton may have an edge in Arkansas. Notably, neither Democrat seems likely to pull out Florida, despite the state's decisive roll in 2000 and 2004. Clinton is stronger v. McCain in equally decisive Ohio, but both Democrats seems likely to win that state at this point in time.
The general election in 2008 for President, of course, will be conducted state by state, so national polls are only dim indicators of a final result. But, polls like this do influence superdelegates who are hungry to win in the general election after losing to George W. Bush the last two times around. Skeptics suggest that McCain's strong support of an unpopular war makes him a hard sell against either Democrat.