Yo! and wellcome to the amiga world :-)
Some advise... Dont use flatscreens with plain AGA get a graphic card and then get a Flat panel.
However i have only tested TFT flat screens and be horenst it looks like ####, manufactures recommends 1078*768 or so.
Any resolution below do work but it's very nasty to look at.
try for yourself, i might be wrong :-)
G'Luck
