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.
GPU clock is 850, memory clock is 1200. according to guiminer-script, it's running at 198kH/s. apparently that is accurate and the number being reported by the pool is not, so your card is 27kH/s faster.