sinong meron ng N91? has anybody tried to successfully install themes and applications in it?

i downloaded some themes and tried to install it in the N91 but it cant do so. downward compatible ba ang N91 vs other Symbian O/S phones? S60 na ang N91. the earlier version, S40, is in 3320, 6020, 6170, 7270 & 7280 models.