From Instant Rails 2.0 to Rails 2.1.0 - cache problem

i'm trying to update to rails 2.1 using instant rails, so i can use
the
new cache features, but when i try to use the method
"Rails.cache.write"
in my controller, i get the message

"undefined method `cache' for Rails:Module (NoMethodError)"

and if i try to set the cache store
("ActionController::Base.cache_store = :memory_store")
in a conf file, i get: "undefined method `cache_store=' for
ActionController::Base:Class (NoMethodError)"

the version message for ("rails -v") is "Rails 2.1.0", so i assume
that
the version is ok. does anyone know what could be the problem? thanks.

double post, please ignore (or delete). i posted
it hours ago through google groups and only now
it appeared. i'll post here directly next time.

Messages from people who have not posted before are queued for
moderation, which will occasionally cause delays.

Fred