High Load And Mysql Errors

My server very slow and the is very loaded. How can I fix this problem? My server specialities and loaded softwares which are below. And sometimes there is "mysql connect failed", "Lost connection to MySQL server during query" errors. Thanks for kinds...

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Speed:
100Mbs

LOAD:
Load avarage : 5-30 +
Cpu usage: %30-95 +
Ram usage: %70-95 +

SYSTEM INFO:
2gb ram, P4 3200 cpu, 2x250 GB SATAII hdd, Plesk 8.1.1, centos 4.5 os, apache 2.0.59, php 4.4.7, mysql 4.1.21(client),
mysql 5.0.41(server), zend optimizer, kernel 2.6.19.1.SM #5 SMP, mod_evasive, plesk firewall, qscanq+clamav,
spamassain and system up-to-date.

SOFTWARE:
phpbb 2.0.22
4images 1.7.4
joomla 1.0.12

ONLINE USER:
100-500 user online
on 2 website

How to optimization?

I installed tuning-primer.sh

but I can’t understand this code:
I don’t know. How to set values, example?
NOTE: Red value

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[root@lavinya bin]# tuning-primer.sh

-- MYSQL PERFORMANCE TUNING PRIMER --
- By: Matthew Montgomery -

MySQL Version 5.0.41-log i686

Uptime = 3 days 4 hrs 34 min 17 sec
Avg. qps = 92
Total Questions = 25406284
Threads Connected = 1

Server has been running for over 48hrs.
It should be safe to follow these recommendations

To find out more information on how each of these
runtime variables effects performance visit:
.............

SLOW QUERIES
Current long_query_time = 5 sec.
You have 115 out of 25406302 that take longer than 5 sec. to complete
The slow query log is enabled.
Your long_query_time seems to be fine

WORKER THREADS
Current thread_cache_size = 8
Current threads_cached = 7
Current threads_per_sec = 0
Historic threads_per_sec = 0
Your thread_cache_size is fine

MAX CONNECTIONS
Current max_connections = 500
Current threads_connected = 2
Historic max_used_connections = 110
The number of used connections is 22% of the configured maximum.
Your max_connections variable seems to be fine.

MEMORY USAGE
Max Memory Ever Allocated : 835 M
Configured Max Per-thread Buffers : 3 G
Configured Max Global Buffers : 46 M
Configured Max Memory Limit : 3 G
Total System Memory : 3.96 G

Max memory limit exceeds 85% of total system memory

KEY BUFFER
Current MyISAM index space = 35 M
Current key_buffer_size = 32 M
Key cache miss rate is 1 : 73658
Key buffer fill ratio = 34.00 %
Your key_buffer_size seems to be too high.
Perhaps you can use these resources elsewhere

QUERY CACHE
Query cache is enabled
Current query_cache_size = 4 M
Current query_cache_used = 1 M
Current query_cach_limit = 1 M
Current Query cache fill ratio = 29.83 %
MySQL won't cache query results that are larger than query_cache_limit in size

SORT OPERATIONS
Current sort_buffer_size = 2 M
Current record/read_rnd_buffer_size = 1 M
Sort buffer seems to be fine

JOINS
Current join_buffer_size = 1.00 M
You have had 14127 queries where a join could not use an index properly
You should enable "log-queries-not-using-indexes"
Then look for non indexed joins in the slow query log.
If you are unable to optimize your queries you may want to increase your
join_buffer_size to accommodate larger joins in one pass.

Note! This script will still suggest raising the join_buffer_size when
ANY joins not using indexes are found.

OPEN FILES LIMIT
Current open_files_limit = 2500 files
The open_files_limit should typically be set to at least 2x-3x
that of table_cache if you have heavy MyISAM usage.
Your open_files_limit value seems to be fine

TABLE CACHE
Current table_cache value = 256 tables
You have a total of 636 tables
You have 256 open tables.
Current table_cache hit rate is 1% , while 100% of your table cache is in use
You should probably increase your table_cache

TEMP TABLES
Current max_heap_table_size = 16 M
Current tmp_table_size = 32 M
Of 2271787 temp tables, 3% were created on disk
Effective in-memory tmp_table_size is limited to max_heap_table_size.
Created disk tmp tables ratio seems fine

TABLE SCANS
Current read_buffer_size = 1 M
Current table scan ratio = 28 : 1
read_buffer_size seems to be fine

TABLE LOCKING
Current Lock Wait ratio =1 : 112
You may benefit from selective use of InnoDB.
If you have long running SELECT's against MyISAM tables and perform
frequent updates consider setting 'low_priority_updates=1'
If you have a high concurrentcy of inserts on Dynamic row-length tables
consider setting 'concurrent_insert=2'.

[root@lavinya bin]#
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if your reply me message I will be happy