I ran into this problem a while ago where css border-collapse:collapse on Internet Explorer 7 and 8 is having a 1px space in between table cells. But its just fine in Firefox, Chrome and Opera. I thought IE8 already has the fix for most IE bugs, well IE ruined my mood again.
Just in case you were having trouble with this one too so here's what I found. On IE7 and IE8, the border-collapse: collapse does not overrule cellspacing even if cellspacing is set to 0. cellspacing should be set to null or empty in order to have it the look it should be.