Um, if you did id3lib installation then it should have put them in /usr/local/lib by default. It's LD_LIBRARY_PATH. Add /usr/local/lib to that and see if that helps you out.

Huh, I tried that (and DYLD_LIBRARY_PATH which I think may be needed for OS X) and it didn't seem to make any difference. I definitely have id3lib installed in that location (I just compiled and installed it) but I am still getting the error below. Anything else I could be missing?

gcc lrc2sylt.c
ld: Undefined symbols:
_ID3Field_SetASCII
_ID3Field_SetBINARY
_ID3Field_SetINT
_ID3Field_Size
_ID3Frame_GetField
_ID3Frame_NewID
_ID3Tag_AddFrame
_ID3Tag_FindFrameWithID
_ID3Tag_Link
_ID3Tag_New
_ID3Tag_RemoveFrame
_ID3Tag_Update