You can deduct losses on Schedule A, or file as a professional gambler with Schedule C.
Might be able to use "Session wins" rather than 1099s as you wins, but I hear conflicting info on this board.
See http://groups.yahoo.com/group/vpFREE/message/104962 for some problems with Schedule C.
http://www.readybetgo.com/book-reviews/review-606.html
How To Turn Poker Playing Into a Business (Knowing What to Deduct to Improve Your Odds With the IRS) by Ann-Margaret Johnston (122 pages, paperbound, $19.95) and The Tax Guide for Gamblers by Roger and Yolanda Roche -- Sixth Edition (64 pages, paperbound, $29.95). Both are excellent references and both are available at Gambler's Book Shop in Las Vegas.
http://www.casinogaming.com/features/taxlaws.html
All winnings from all forms of gambling are taxable and must be declared as income on your tax return.
All losses from all forms of gambling are deductible as an itemized deduction for recreational players, limited to the amount of winnings declared.
Professional gamblers hold file as a self-employed business using Schedule C.
The value of "comps" received are considered to be gaming winnings and should be included in your total winnings. This does allow you to deduct gaming losses to offset the income from the "comps."
Wins and losses are reported only in the year they occur. Excess losses cannot be carried forward or back to offset winnings in other years.
Married couples filing a joint return must combine their winnings and combine their losses, and report only one figure for each.
The IRS has issued instructions that "lumping" is unacceptable. "Lumping" is the practice of reporting one net win figure and no losses, or reporting nothing if your net from gambling is a loss. You must report the total of your winning sessions separately from the total of your losing sessions.
The IRS requires that an accurate diary or similar record must be maintained for substantiating your wins and losses, and that the diary should contain at least the following information: (1) the date and type of your specific wager; (2) the name of the gaming establishment; (3) the address or location of the gaming establishment; (4) the names of the other person(s), if any, present with you; (5) the amount(s) you won or lost.
The IRS also requires that in order to substantiate your diary, supplemental records are required, including the following (these records are not to be submitted with your return, but will be needed should you be audited): (1) W-2Gs; (2) wagering tickets or receipts; (3) canceled checks; (4) credit card records such as cash advances; (5) bank withdrawals; (6) any receipts provided by the gambling establishment.
KEEP RECORDS OF YOUR GAMBLING TRANSACTIONS
In February of 1998, in a case involving an unemployed gambler who failed to file timely returns for two years and kept no records, the Tax Court ruled that the gambler could not deduct unsubstantiated gambling losses. In addition the Tax Court upheld the IRS which had levied additional amounts for failure to file on time and for the accuracy-related negligence penalty. This increased the gambler's tax liability by 43%!
In other words, they threw the book at this gambler, who actually told the court that although he maintained a gambling log for one of the years in question, it was not accurate because it was too time-consuming to make it precise.
If you are collecting W2-Gs and not keeping accurate records, this very well could be in your future.
<many more details on the webpage>
http://www.irs.gov/taxtopics/tc419.html
You may deduct gambling losses only if you itemize deductions. Claim your gambling losses as a miscellaneous deduction that is not subject to the 2% limit on Form 1040, Schedule A (PDF). However, the amount of losses you deduct may not be more than the amount of gambling income reported on your return. It is important to keep an accurate diary or similar record of your gambling winnings and losses. To deduct your losses, you must be able to provide receipts, tickets, statements or other records that show the amount of both your winnings and losses. Refer to Publication 529, Miscellaneous Deductions, for more information.