Linux System Freeze

oracle 11g on 1g of ram? that's all i'm thinking, i know you mentioned a lot of swap.. but still.
can you use top or glance and see if using a ton of I/O during the time..

I know of incident with oracle 8, when and index got erased. the i/o went thru the roof and exhibited the same thing on much higher end machines.... took 6 hours for a gracefull shutdown.
thinking of that , make sure your querries are optimized so that not using a lot of io.