The maximum contributions that can be made to health savings accounts in 2010 will increase as will the minimum deductible imposed by health insurance plans linked to HSAs and the maximum out-of-pocket expenses that employees can be required to pay.
The maximum contribution that can be made to an HSA in 2010 for employees with single [...]

In Administrative, Procedural, and Miscellaneous Notice 2004-50, the IRS addresses this question. See Questions 2 and 4, excerpted below:
 Q-2. May an otherwise eligible individual who is eligible for Medicare, but not enrolled in Medicare Part A or Part B, contribute to an HSA?
 A-2. Yes. Section 223(b)(7) states that an individual ceases to be an eligible individual [...]

If your spouse is enrolled in a Health Care FSA, you are not eligible to contribute to a Health Savings Account. The FSA is available to spouse and tax dependents of the person with the FSA. It can be used for the same medical expenses as the HSA. As a result, you cannot contribute to [...]

Employees who are enrolled in the High Deductible Health Plan (HDHP) are eligible to contribute to an HSA.  The employee can not be enrolled in any other health plan coverage that provides medical benefits before the HDHP deductible is met, not claimed as dependent under someone else’s tax return, and not enrolled in Medicare.

Frequently Asked Questions – Health Savings Accounts

Contributions
Reimbursements
Taxes