The UI design pattern you're looking for is (generically) referred to as Master-Detail.
Take a look at Todd Geist's 2 versions (Master Detail and MasterDetail 2.0) over at the Modular FileMaker site. They perform well on large datasets and even respect the current sort order. I prefer his original method, particularly if you base your virtual list on an unstored Get(RecordID) — see Daniel Wood's comments under the Hyperlist module — for superior performance in hosted solutions. (And while you're over at Modular FileMaker, take a look at the couple dozen or so other excellent modules that developers have contributed; it's an invaluable resource for FileMaker development.)
(P.S. Siplus - thanks for your file, too. I'm about to download and am eager to see/compare your approach. The more options, the better!)
thanks Mark, will have a look but siplus's is that easy !