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If you sold part of your property - you need to report that sale transaction in the year the property was sold. Thus if the sale transaction was completed in 2011 - that should be reported on 2011 tax return.
When you will sell the other part of the property - you will report another sale transaction. If you sell part of your property - you need to prorate the basis as attributable to that part.
If you qualify to exclude the gain on the sale of your primary home - you do not need to report that transaction on your tax return - please see for reference IRS publication 523, page 19 - www.irs.gov/pub/irs-pdf/p523.pdf
Do not report the 2011 sale of your main home on your tax return unless:
You have a gain and do not qualify to exclude all of it,
You have a gain and choose not to exclude it, or
You received Form 1099-S.
Otherwise, report the sale on your tax return. Report the sale on line 1 or line 3 of Form 8949 as a short-term or long-term transaction, depending on how long you owned the home. Complete columns (a) and (c) through (f) as you would if you were not claiming the exclusion. Enter the selling price (Worksheet 2, line 1) in column (e) (other than the portion of the selling price allocated to business or rental use). Enter the adjusted basis (Worksheet 2, line 4) in column (f) (other than the portion of the adjusted basis allocated to business or rental use). Enter "H" in column (b) if you are excluding any gain reflected on Form 8949. Include in column (g) as a negative number (in parentheses) the amount of any such excluded gain (and any selling expenses other than those allocated to business or rental use). See the example for column (g) in the Instructions for Schedule D (Form 1040).
If you use exclusion - you generally will not be able to claim another exclusion for two years. Only after two years you will be eligible to claim another exclusion.
See for reference in the same publication page 10:
You can exclude up to $250,000 of the gain (other than gain allocated to periods of nonqualified use) on the sale of your main home if all of the following are true.
You meet the ownership test.
You meet the use test.
During the 2-year period ending on the date of the sale, you did not exclude gain from the sale of another home.
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