autovacuum fringe case?

I have a server that is IO-bound right now (it's 4 cores, and top
indicates the use rarely hits 25%, but the Wait spikes above 25-40%
regularly).  The server is running postgresql 9.0 and tomcat 6.  As I
have mentioned in a previous thread, I can't alter the hardware to add
disks unfortunately, so I'm going to try and move postgresql off this
application server to its own host, but this is a production
environment, so in the meantime...

Is it possible that some spikes in IO could be attributable to the
autovacuum process?  Is there a way to check this theory?

Would it be advisable (or even permissible to try/test) to disable
autovacuum, and schedule a manual vacuumdb in the middle of the night,
when this server is mostly-idle?

Thanks for any tips.  I'm in a bit of a jam with my limited hardware.

-AJ