While table cells in HTML may look like block elements, they’re not, and thus you can’t absolutely position things inside them. I’ve been using a script that I’ve had for ages to get around this. The script would add a helper div around the contents of every cell that was relatively positioned. The benefit of my old script was that it was library independent. The drawback was that it was long, I don’t know who wrote it, it added a div to every TD and TH, and it resisted all efforts to make it target only tags with specified classes.
I retired that script today in favour of iWouldLikeToAbsolutelyPositionThingsInsideOfFrickingTableCellsPlease() over at CSS-Tricks. I renamed it to cellPos(), though.