With Mark to Market, a Trader treats securities gains and losses as ordinary gains and losses (except for any separate investment securities they may have.) In effect, your gains are taxed as ordinary gains and your losses are allowed in full in the year they are incurred. It's complicated to change to Mark to Market as you must also change your accounting method. See the IRS description here: <a href="
http://www.irs.gov/taxtopics/tc429.html" rel="nofollow" target="_blank">
http://www.irs.gov/taxtopics/tc429.html</a> I would never recommend someone doing it without professional help.
For gains and losses in your situation, you would report your stock gains and losses as if you were not a day trader. In effect, you would enter them the same as anyone else. You would also need to create a separate schedule C (business) where you would report no income, but would deduct margin interest and any other direct costs you may occur. Unlike an investor, these would be business expenses, not itemized deductions.
As you're moving into a complex field professional help, at least for the first year, might be in order.
