eMac OS9 Display Problems

I have an emac ati graphics 1ghz dual booting os 9.2.2 and OSX 10.5.8 when i boot into os9 there is a massive black border around everything and the actual viewable part of the screen is tiny. how can this be fixed?

eMac serial *vm******p9l*

512mb ram (originally 128mb)

160gb HDD (originally 60gb)

DVDRW drive (originally dvd rom cdrw combo)

1ghz powerpc g4

ati 7500 32mb graphics

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