When you say "table" are you referring to a tabbed text table, as in Quark 3,4, 5 and 6, or a collection of text boxes, in the new Table item (Quark 5 and 6)?
If the former, you have to adjust your tab columns so that the fill characters are ". " (period and space) which will automatically fill out the gaps between columns with leaders. The last column will need probably an "option-tab" (at least that's what it is on the Mac) to fill out the rest of the line.
If it's the Box-type tables, perhaps you could define tabs within each column, and use the fill character setting to supply the leaders. I haven't found the box-tables as useful for my clients, so I don't have a whole lot of suggestions on this, sorry.
G