Apache2 tuning needed?

Hi all,

I've got a problem with a server. It's a low end server, about 150
vhosts. 512 Mb ram.

I get server running very slow. I see:

Current Time: Monday, 21-Nov-2005 21:50:15 CET
Restart Time: Monday, 21-Nov-2005 20:00:15 CET
Parent Server Generation: 0
Server uptime: 1 hour 50 minutes
Total accesses: 18061 - Total Traffic: 119.2 MB
CPU Usage: u14.61 s5.02 cu.01 cs0 - .298% CPU load
2.74 requests/sec - 18.5 kB/second - 6.8 kB/request
81 requests currently being processed, 11 idle workers


top - 21:55:16 up 14:54, 2 users, load average: 72.25, 63.02, 54.48
Tasks: 149 total, 2 running, 147 sleeping, 0 stopped, 0 zombie
Cpu(s): 4.3% us, 5.3% sy, 0.0% ni, 0.0% id, 88.7% wa, 1.3% hi,
0.3% si
Mem: 516104k total, 483548k used, 32556k free, 1936k
buffers
Swap: 19535032k total, 3370500k used, 16164532k free, 8708k cached


vmstat
procs -----------memory---------- ---swap-- -----io---- --system--
----cpu----
r b swpd free buff cache si so bi bo in cs us
sy id wa
1 44 3413448 32708 1900 9240 260 390 315 449 783 31 15
2 71 11


A very high value of WA time. No error logged from kernel, no
OOM-Killer in action.

Why apache got a so high value of WA time? It's only a problem of sites
tuning?

I'm running apache 2.0.54 from debian sarge stable packages.

Thanks
Stefano