limiting rows and pages like google

Hi, I am trying to find out the the best way to do the following: I have a script that select records from a table. The problem is that I need to limit the rows to 20. I know that I can use limit 20. But what I want to do is give the view a link to the next 20 till all the records are shown. What I don't know is how to maintain the search query and I want to use the same script. The logic would be to check if the script is called the first time, then the sql statement would be select travel.*, city.city from travel, city where travel.cityid=city.id limit 0,20. The second time or based on what has been selected on the page (1-20, 21-40, etc) add that to the sql statement. My question is how? Can someone guide me or give me some example. TIA Adrian