If the load cell must be read by the Arduino then see http://cerulean.dk/words/?page_id=42
for an example. It's not too hard to get right; the most problematic part is getting the gain set correctly. You'll want to use some sort of low value trimmer to get it right. Also, you'll be limited by the precision of the Arduino's A/D converter (10 bits) unless you use an external, higher precision A/D converter.
You still need the load cell of course, and extracting it from a scale like John linked is still a good idea.