Just to get going quickly, I downloaded guiminer-scrypt and joined wemineltc.com. My 5770 is running at around 300 kH/s, generating around .5 ltc per day. It was very easy to get it working.
Edited to clarify that I used guiminer-scrypt, since it's different from guiminer.
What is your core and memory? I have 6770 and I have 225 kh/s 985-1200.
I'll check when I get home, don't recall the exact numbers. I think the guiminer is reporting 200 kH/s, but my stats on wemineltc.com are a bit higher, although it fluctuates between 200k and 400k, typically around 300k.