Your broker should be able to help you specify which shares you want to sell, but that is usually done for tax purposes really (for example, if you had purchased shares in May '08, December '08 and May '09, you might elect to sell your May '08 shares since those would represent a capital gain vs. the others which are short term gains currently).
On your tax schedule, you total purchases together and sells together, so that if in this calendar year you spent $10,000 on SPNG purchases and netted $25,000 from SPNG sells (long term together and short term together), you would have a $15,000 gain, regardless of which shares you had remaining.
This is a crude explanation, but I hope it helps!
