swap size

[Max <davros@cyclone.Stanford.EDU>]

I'm about ready to setup a machine with 512 MB of RAM and I'm
wondering how much swap space I should allocate.  I've read about the
2x rule, but 1 GB of swap seems somewhat excessive.  I've also been
told that Linux will not use more than 128 MB of swap.  So, how much
should I allocate?  Can I change it later without having to reinstall
everything?  The machine is a dual-processor workstation that will be
used by 4-8 people concurrently for number crunching and all sorts of
simulations.

Also, is it possible to put /tmp within swap?  Is that the default?

Thanks,
    Max