I can't answer your question, but here is something that may be of interest. Also,
not sure about Win7, but on WinXP, during compiling of a sketch, the core.a file
gets written into a "temporary" folder. Note - when you leave the IDE, all the files
in the folder are erased.
On WinXP, you can find this folder under
c:\Documents and Settings\user_whoever\Local Settings\Temp, and it will have a
folder name something like "build435841510710457.tmp". You might look in there,
and also at the Property settings of the folder. If nothing else, it's interesting to know
where this folder is located.