Get your taxes done using TurboTax

@martin :  The Sales Schedule should spell out what the right Cap Gain is if you work across the columns.  But here's an example:  

You bought for $10,000.  You sold for $15,000.  The K-1 says you had "Cum Adjustments" of -$4000.  
So your Total Gain is ($15,000 - ($10,000-$4000)) = $9,000.  

But the IRS taxes that at two different rates.  Part of it is at Cap Gain rates, and part of it is at Ordinary Income rates.  So the Total Gain of $9000 has to be split, which is why the K-1 will tell you that, for example, $3500 is Ordinary Gain.

So now your $9000 Total Gain splits into $3500 Ord Gain and $5500 Cap Gain.  
The $3500 should be on Form 4797
The $5500 is what needs to be on the 1099-B
So what basis goes on the 1099-B?  Well, it shows $15,000 as Sale Proceeds, and you want Cap Gain of $5500, which means your basis is $9,500.  So that's what you enter on the 1099-B.

Note that the $9500 basis can be arrived at differently:
Purchase ($10000) - Adjustments ($4000) + Ordinary Gain ($3500).  But that's not a very intuitive formula.  And its easy to get wrong (as I did when I wrote it a couple comments ago)...