Amiga500's as long as you've got a "Fatter Agnus" (1 meg chip I believe is the distinguishing feature) can swtich from NTSC to PAL. There are some software that will do that for you. I used to boot a disk (called "TurboPal") that would load up quickly, give you and option for NTSC/PAL, how much chip ram and I believe the option to turn off fast ram or not.
From growing up games generally played okay in NTSC or PAL. Playing PAL games in NTSC generally had faster music, and you might loose some of the screen as the PAL resolutions are larger. You'll also see a faint flicker.
Playing NTSC games in PAL generally would have black borders around the screen (smaller resolution) and the music would generally play slower.
The disk also worked with an A1200 but cut down the Chipram to 1meg.
It's not really needed because of the early startup menu.
Umm, I don't know if there's a jumper or anything you can do to set the default from NTSC to PAL in the case of the A1200 and A500.
As for scandoubler + SVGA monitor, I would say that it depends on the monitor, and scandoubler. Although I'm in Canada, I've set my A4000 to PAL (A4000's and A3000 have a jumper on the board to set this) and the Phase5 scandoubler takes both NTSC and PAL resolutions well (on a very old VGA monitor). However, since Phase5 was in Germany, I'd wager it worked great. Umm... The A3000's flicker fixer also worked great.
If you want to check out your A1200 + Scandoubler I'd say just plug everything in, go into the early startup menu and then press a key to toggle between "PAL" and "NTSC", if they both show up then you're fine.
