This is my 960 grid system case:
ID
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With using the inline-block it will behave as an inline object. so no floats needed to get them next to eachother on one line. And indeed as Rito said, floats need a "body", like they need dimensions.
I totally agree with Pekka about using tables. Everybody that build layouts using div's avoid tables like it's a desease. But use them for tablular data! That's what they're ment for. And in your case i think you need them :)
BUT if you really really want what you want. There is a css hack way. Same as the float hack.
.kundregister_grid_1:after { content: "."; }
Add that one and you're also set :D (Note: does not work in IE, but that is fixable)