Hello Katie,
Sorry to hear you are having problems. Hope I can help.
Firstly clamps - When setting up the machine to use the ribber you have a second pair of clamps which you use to secure the main bed in a raised position. The clamps which were originally in use on the main bed are now used to secure the ribber. At each end of the ribber bed behind the side levers there is an arm which folds down and rests on the table. Use the flat clamps to secure these arms to the table.
You do not say the make of your machine. Toyota ribbers do not need adjusting but you need to make sure the ribber sits snugly against the main bed before you tighten the setting screws. Brother ribbers can be adjusted - the instructions are in the ribber book. To get the spacing correct you have to slide two claw weight hangers between the main bed needles and the sinker posts of the ribber. They should fit snugly WITHOUT pushing up the needles. Err on the side of it being a bit low as often when you tighten up the adjusting nuts the ribber rises a bit. Hope this helps - I'm sorry but I do not have any experience of Knitmaster machines.
Sue
February 2010