You won't encounter many problems with an
NTSC machine but you may have to select PAL
mode from the early startup menu or use
a PAL boot disk of some kind to get certain
games that require PAL mode to work.
Also, remember that TVs in north america generally
can't display PAL mode, so you will need a
1084 or better monitor or possibly some
composite monitors will be OK. In any case
you can switch between NTSC and PAL quite
easily on an A1200 from the early startup.
(hold down both mouse buttons when turning on)
Also, many of the old floppy games can be
installed to the harddrive now using JST or
WHDLoad from aminet and the associated installs
that use them...