comparing logic

Hi, querying the database with a condition (select * from packages where mb>=5 and price<=5 and os=linux) I am displaying the result in a table with a checkbox at the side of each row which has its own unique $id_no I want give the client/visitor a chance to be able to compare plans (max upto 5 plans) hence building a query like this select * from packages where $id=$id_no1 and $id=$id_no2 and $id=$id_no3 and $id=$id_no4 and $id=$id_no5 but how do know if the client will want to compare just 2 plans or more or all 5? and lastly how can i make sure if he picks more than 5 comparisions it will still only compare the first 5? I know arrays are involved but although i love PHP I HATE arrays as i always get confused with them even after going through arrays in the manual and in my "php blackbook". Kindly help. Thanks, -Ryan