Sorry;  Things might have changed but as afr as I know

Trade Date rules.

Why????

Because this is the date you no longer are an economic owner of the asset.

Huh??

Well this means  that if you sell something today to settle 1 month from now then while you might ophysically be holding the shares for interest and divedend you DO NOT have a risk positoin for capital gains

As such whle interest or dividends earned between trade date and ssettlement date are

 reportable there is NO no longer any principal at risk ( i suppose if you sold the stock 

to your cousin jane then maybe you can say there is some counterparty risk and delay the gain untill settlment) 
But since I'm refering to exchange traded assests then your exposure is elimiated and your P&L locked in on Trade date and that is the date  on which you report gains and losses.

This year any sale made until  3:59:59 on 12/31/07 may be reported as  a capital gain/loss in 07 ( although I also beleive the tax code gives you the option to report in 2008)

 But don;t beleive me check your 1099-B