if i remmeber rightly, the max SGA size on 8.1.7 is 1.75 Gb unless you relink your libraries with some flag.

So use 1.75 Gb :-)

On our we use about 100Mb for shared pool unless you have heaps and heaps of pl/sql code.

Do you use java, if so set your java pool

use majoirty on block buffers

This assumes one instance and having an app that doesnt require gobs of RAM