LinuxQuestions.org - server slow

hi friend,
i have installed redhat Cent O.S 4.2 on my sever.

while client is accesing its homepage , it has a slow response.when client use ftp for file transfer, response from server is slow.
i am running php software and MYSQL database in my server.
i am using 80GB hard disk and still 28GB freespace is remaining.
i have 512 MB of memory, in which currently 91 MB is still free.
o/p for " vmstat" command is
"procs -----------memory---------- ---swap-- -----io---- --system--

----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
0 0 160 91296 40656 287300 0 0 9 7 60 34 0 0 100 0"
o/p for "free" command is

"total used free shared buffers cached
Mem: 507932 416572 91360 0 40636 287284
-/+ buffers/cache: 88652 419280
Swap: 779144 160 778984"
o/p of "top" command is
"top - 14:31:52 up 2 days, 1:12, 2 users, load average: 0.00, 0.00, 0.00
Tasks: 74 total, 1 running, 73 sleeping, 0 stopped, 0 zombie
Cpu(s): 1.7% us, 0.0% sy, 0.0% ni, 98.3% id, 0.0% wa, 0.0% hi, 0.0% si
Mem: 507932k total, 416772k used, 91160k free, 40612k buffers
Swap: 779144k total, 160k used, 778984k free, 287268k cached"
In the /var/log/messages there are no errors
But in the /var/log/httpd/error_log it is showing a long list of same error i.e" an unknown filter was not added :PHp".in this way my server is responding very slow for ftp and while accesssing through http.
i am using php application of client-server type.

for the information abt network,
i have the o/p of some standard commands as,
1.for "mii-tool eth0"
o/p-
"eth0: negotiated 100baseTx-FD, link ok"

2.for"ethtool -S eth0"
o/p-
"NIC statistics:
early_rx: 0
tx_buf_mapped: 0
tx_timeouts: 0
rx_lost_in_ring: 0"
3.for "netstat -i"
o/p-
"Iface MTU Met RX-OK RX-ERR RX-DRP RX-OVR TX-OK TX-ERR
TX-DRP TX-OVR
Flg
eth0 1500 0 43568 0 0 0 41105 0

0 0
BMRU
lo 16436 0 22 0 0 0 22 0
0 0
LRU"

i have rebooted the server today and then check the response of http

and ftp , that response is better than the previous 3 days,for http

request , it was taking a minute to open the link yesterday,which is

now opening in seconds.but still iam unknown of the cause for such a

response of server.if server starts responding same as it was

responding since last three days, then what action should i take.will u

pls help me to solve this problem?