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.
Hi
I also have a 5770 and do about 200 or so Hashes.. So 300K is very very very good!
Did you overclocked it? What settings are you using?
regards,
P