how about...
select .... where translate(lower(myfield), 'âãäåāăąèééêëēĕėęěìíîïìĩīĭóôõöōŏőùúûüũūŭů', 'aaaaaaaeeeeeeeeeeiiiiiiiiooooooouuuuuuu') = 'stringiwannamatch';
or something like that. I may have miscounted the vowells in the 'to' string :)