Are you using the -m parameter of spamd to limit the number of children it will spawn? I'd suggest something like -m 6 to start with.
Yeah it is setup for 50:
-d -c -a -m50 -u user -v -H
50 is a LOT of spamd's... even at the low-end of 15mb each that's 750mb of memory allocation.
Since your box has 256mb of physical ram, I'd limit it to maximum of 256mb/15mb = 17 spamd's at the highest. I'd really suggest using something much lower like 10 unless you add some ram.
