I think eried is slightly mistaken - its the lilypad bootloader that uses the internal 8MHz oscillator.
If you want to uses a 32kHz crystal, common for clock applications, check out this thread on ladyada's forum - the code I give has the registry settings you need to use a 32kHz crystal to keep time...
http://www.ladyada.net/forums/viewtopic.php?f=22&t=4418&start=15