hi,
you can try several things
1. reduce to minimum following init.ora parameters that affect
size of memory for new session:
- bitmap_merge_area_size
- create_bitmap_area_size
- hash_area_size
- sort_area_size (biggest memory consumer)

2. Disable OTRACE, which is enabled by default
- stop oracle database
- go to $ORACLE_HOME\otrace\admin and delete all files
with a '.dat' extension.
- restart database

3. Increase the amount of swap space.

4. Consider switching to Oracle Multi Threaded Server (MTS).

Regards,

dave777