Basically what you're going to do is allocate more RAM to Java which will let your RS run smoother.
First thing you should do is download the official rs client from
http://www.runescape.com/kbase/guid/Downloads_and_WallpapersAfter installing, hit start and search for 'runescape.prm' , this should only give 1 result (
http://puu.sh/7WZk)
Open the file with notepad, you should get this:
http://puu.sh/7WZNNow what you want to do is change the '128' in the 2nd line from the bottom to a higher number; this is the MB of RAM allocated to Runescape on your pc. I personally advise not allocating more than 1/3rd of your total RAM if you have 2GB+ RAM, or not more than 1/4th if you have below 2GB. I personally use 1gb out of 4 for RS and my scape runs perfectly smooth on maxed settings (with 1 second loading screens).
Assuming 1 gb, change the 128 to 1024 giving this:
http://puu.sh/7X0VSave the file, close it, and re-load the official rs client.
Enjoy smooth scaping.