[spider]

Check w/ your broker b/c there are a lot of differences here, but I believe the default assumption at most is FIFO (first in first out) which is what you want here. I know Scottrade is like that. Etrade will let you specify which lot to sell at the time you sell. You can also do this with Scottrade but you actually have to do it over the phone.

Check the IRS pubs (google something like "tax lot capital gains") but the gist of it is you need acknowledgement from your broker at time of sale -- you can't wait until tax time to do it since that would let you game the system.