postgresql and apache slow down

hi guys,
I'm preparing a new server to host some website postgresql+php4+apache
1.3.x based.

the machine's hardware configuration is:

* amd sempron 3200+ native 64bit
* 1 GB ram DDR2
* chipset nvidia geforce 6100
* controller sata2 silicon image 3112 with RAID functionality
* 2 sata2 hard disk western digital

the machine's software configuration is:

*debian etch 4.0 last snapshot
* apache 1.3.34
* php 4-4-4
* php4 pgsql connector
* postgresql 8.2.1 compiled from source

The machine is on my LAN 100 Mbps.
I've put a simple drupal site 4.7.x for benchmark purposes.

trying for another machine (but from the same too) ab with concurrency
50 and 2000 requests I got an enormous RAM consunption from apache and
postgres processes.
The machine begin to swap heavily and the only solution is to stop
apache and postgresql processes to regain the control of it.

The same test on my production machine (debian sarge 3.1, postgresql
8.1.6 from source) don't have problem.

What can be the cause of this crazy behaviour?

Best Regards
Federico Campoli