Mysql full text search cause high usage CPU

We built a news site. Every day we will input tens of thousands data from web api.

In order to provide a precision search service, our table use MyISAM, build fulltext index (title, content, date). Our site now test in Godaddy VDS with 2GB RAM, 30GB space (No swap, because VDS do not allow to build swap).

with #grep “model name” /proc/cpuinfo we get Godaddy use Intel(R) Xeon(R) CPU L5609 @ 1.87GHz

Here is our mysql input, use FROM dual avoid insert duplicate record, and the table's FULLTEXT index always on.

INSERT INTO newstable
(title,link,content,date,source,image,imagesource) 
SELECT '".$title."','".$link."','','".$content."','".$date."','".$source."','".$image."','".$imagesource."' 
FROM dual WHERE not exists 
(SELECT content FROM newstable WHERE newstable.content = '".$content."')

Here is our search query in the reading page (We have optimization the home page, it is a static page， be generated from crond, but the reading page should keep in for a live search):

SELECT  id,title,link,content,date,source,image,imagesource 
FROM newstable 
WHERE (MATCH (title,content,date) 
AGAINST ('$boolean' IN BOOLEAN MODE)) 
Order By date DESC Limit '.($_POST['number']).', 10

each page have 2 or 3 queries like above. (* I have renamed table name and field name)

For a news site, we need keep fresh news on the top site, so sort by date is required.

Now, our problem is: Mysql full text search will cause high usage CPU. use #top for a server monitoring, open each page will cost neally 10% CPU. I am afraid in this case, our site could only support few people online at the same time. But our goal is 100 people online at the same time at least. Many Thanks.

Cpu(s):  10.4%us,  1.4%sy,  0.0%ni, 88.5%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:   2097152k total,   570364k used,  1526788k free,        0k buffers
Swap:        0k total,        0k used,        0k free,        0k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
28265 mysql     15   0  385m  75m 5752 S 129.3  3.7 751:49.13 mysqld
 1313 root      15   0 35040  18m 6400 S  7.0  0.9   0:03.55 php
    1 root      15   0  2156  664  576 S  0.0  0.0   0:04.42 init
 1215 root      15  -4  2260  652  436 S  0.0  0.0   0:00.00 udevd
 1359 root      15   0  2240 1004  812 R  0.0  0.0   0:00.00 top
 1585 root      25   0  2832  868  700 S  0.0  0.0   0:00.00 xinetd
...

EDIT: explain query result:

id  select_type table   type    possible_keys   key key_len ref rows    Extra
1   PRIMARY newstable   fulltext    index_name  index_name  0       1   Using where

EDIT2: ./mysqltuner.pl result

-------- General Statistics --------------------------------------------------
[--] Skipped version check for MySQLTuner script
[OK] Currently running supported MySQL version 5.5.20
[OK] Operating on 32-bit architecture with less than 2GB RAM

-------- Storage Engine Statistics -------------------------------------------
[--] Status: -Archive -BDB -Federated +InnoDB -ISAM -NDBCluster
[--] Data in MyISAM tables: 396M (Tables: 39)
[--] Data in InnoDB tables: 208K (Tables: 8)
[!!] Total fragmented tables: 9

-------- Security Recommendations  -------------------------------------------
[!!] User '@ip-XX-XX-XX-XX.ip.secureserver.net'
[!!] User '@localhost'

-------- Performance Metrics -------------------------------------------------
[--] Up for: 17h 27m 58s (1M q [20.253 qps], 31K conn, TX: 513M, RX: 303M)
[--] Reads / Writes: 61% / 39%
[--] Total buffers: 168.0M global + 2.7M per thread (151 max threads)
[OK] Maximum possible memory usage: 573.8M (28% of installed RAM)
[OK] Slow queries: 0% (56/1M)
[!!] Highest connection usage: 100%  (152/151)
[OK] Key buffer size / total MyISAM indexes: 8.0M/162.5M
[OK] Key buffer hit rate: 100.0% (2B cached / 882K reads)
[!!] Query cache is disabled
[OK] Sorts requiring temporary tables: 0% (0 temp sorts / 17K sorts)
[!!] Temporary tables created on disk: 49% (32K on disk / 64K total)
[!!] Thread cache is disabled
[!!] Table cache hit rate: 0% (400 open / 298K opened)
[OK] Open file limit used: 41% (421/1K)
[!!] Table locks acquired immediately: 77%
[OK] InnoDB data size / buffer pool: 208.0K/128.0M

-------- Recommendations -----------------------------------------------------
General recommendations:
    Run OPTIMIZE TABLE to defragment tables for better performance
    MySQL started within last 24 hours - recommendations may be inaccurate
    Enable the slow query log to troubleshoot bad queries
    Reduce or eliminate persistent connections to reduce connection usage
    When making adjustments, make tmp_table_size/max_heap_table_size equal
    Reduce your SELECT DISTINCT queries without LIMIT clauses
    Set thread_cache_size to 4 as a starting value
    Increase table_cache gradually to avoid file descriptor limits
    Optimize queries and/or use InnoDB to reduce lock wait
Variables to adjust:
    max_connections (> 151)
    wait_timeout (< 28800)
    interactive_timeout (< 28800)
    query_cache_size (>= 8M)
    tmp_table_size (> 16M)
    max_heap_table_size (> 16M)
    thread_cache_size (start at 4)
    table_cache (> 400)

EDIT 3: my.cnf

[mysqld]
port            = 3306
socket          = /tmp/mysql.sock
skip-external-locking
key_buffer_size = 256M
max_allowed_packet = 16M
max_connections = 1024
wait_timeout = 5
table_open_cache = 512
sort_buffer_size = 2M
read_buffer_size = 2M
read_rnd_buffer_size = 2M
myisam_sort_buffer_size = 128M
thread_cache_size = 8
query_cache_size= 256M
# Try number of CPU's*2 for thread_concurrency
thread_concurrency = 8
ft_min_word_len = 2
read_rnd_buffer_size=2M
tmp_table_size=128M