The IRS ruled that bitcoins and other cryptocurrencies are property, not currency. As such, you determine gain or loss in the same was as any other type of property. Compare what you paid for the bitcoins and what you received on the sale (making adjustments for commissions, etc.).
For calendar year 2007, taxpayers covered by an HDHP may contribute up to the lesser of the annual deductible or $2,850 ($5,650 for family coverage).