The quick solution: boot in safe mode (just like a real Mac - hold the shift key until the silver screen with your disks in the center appears). You can type commands at this point which are arguments to the Chamelon boot loader: in this case try:
WakeImage=(name of a non-existant file) - then hit return
You should now have booted normally...
Longer-term solution: conce you can startup and login normally, the following commands in a terminal:
sudo pmset -a hibernatemode 0
sudo rm /var/vm/sleepimage
i.e turn hibernation off (should still sleep OK on lib close etc) and also free disk space by deleting the hibernation image file (roughly the size of your RAM).