If your PC's graphics card has tv-out, it's possible to use this in conjunction with UAE in fullscreen mode.
I do this for MAME32 and Snes9x, works a treat.
I have a real A1200 so haven't actually tried UAE on tv-out, but everything else I've tried works so far. Just make sure you match UAE's output resolution to the same as the desktop in tv mode (800x600 in my case).
Useful link for Nvidia owners with tv-out cards: www.tvtool.de
(contrast/overscan/hotkeys manipulation - far better than the NV detonator tv tab.)