Running both PG 8 and PG 9

Hi all,

I just installed PG 9 on my Macbook (enterprisedb) just to start playing
around with it. My Postgres 8.4 installation won't start now anymore, it
is complaining about shared memory already being in use.

Is it even possible to run PG 8 and PG 9 side by side? I was under the
impression this was possible provided they listen on different ports?

Thanks,

Bastiaan Olij