Memory Settings

Hi
I'm having speed problems with my java application which uses Oracle 8i DB.
I Think that it has to be something with the memory preferences,
anyway, my question is, by what do i choose the db memory size?
when i use DBA Studio, it shows 4 types of memory(Buffer Cache,Java Pool, Shared Pool, Large Pool) how do i decide how much each type gets?

and i also have another question regarding OMS(Oracle Manangment Server).
i want to export my tables from the db so i could have a backup,
but when i try to do this using DBA Studio it says i have to be connected to OMS, when i try to connect to OMS it says it couldnt find an OMS Server on the host given(the oracle db is on that host).
eventually i found out that there's a service called OMS on that host
but it isnt runing, when i tried to start it, it didnt work saying there's a file missing, my question on this subject is, can i somehow install the OMS so it will work?

Thanks For all your Help