Slow, high load, Performance issue

[brainslush]

Hey, I've a problem...
I've a lot of performance problems since I've installed Joomla on my VServer. Every time when I try to login into Joomla it takes around 30seconds to process the login and "top" shows me a cpu-load of 13% "php5-cgi" (the highest I can get, means 100%). The front-page is offline so there can't be anyone else who is accessing the webpage at the same time.

My system:

OS: Debian Lenny
RAM: 1GB save, 2GB dyn.
CPU: 384 MHz of a 8 Cores Intel Nehalem processor

I already switched between fcgid and fastcgi but it didn't solve the problem

/etc/ispcp/apache/working/fastcgi_ispcp.conf
/etc/apache2/mods-available/fastcgi_ispcp.conf

Code:

<IfModule mod_fastcgi.c>
    FastCgiWrapper On
    FastCgiIpcDir /var/lib/apache2/fastcgi2

    FastCgiConfig -minProcesses 1 \
                  -maxProcesses 400 \
                  -maxClassProcesses 5 \
                  -multiThreshold 80 \
                  -killInterval 60 \
                  -startDelay 5 \
                  -idle-timeout 300 \
                  -singleThreshold 100
                  # -autoUpdate \
                  # -pass-header HTTP_AUTHORIZATION

    FastCgiServer /var/www/fcgi/master/php5-fcgi-starter -user vu2000 -group vu2000 -idle-timeout 300

    #
    # PHP5 SUPPORT
    #

    AddHandler php-fastcgi .php .php5

    <Location /php5/php5-fcgi-starter>
        SetHandler fastcgi-script
        Options +ExecCGI
    </Location>

    Action php-fastcgi /php5/php5-fcgi-starter
    AddType application/x-httpd-php .php .php5
</IfModule>

/etc/apache2/mods-available/fastcgi.conf

Code:

<IfModule mod_fastcgi.c>
  AddHandler fastcgi-script .fcgi
  FastCgiWrapper /usr/lib/apache2/suexec
  FastCgiIpcDir /var/lib/apache2/fastcgi
</IfModule>

php5-fcgi-starter

Code:

#!/bin/sh

umask 022

PHPRC="/var/www/fcgi/domain.de/php5/"
export PHPRC

TMPDIR="/var/www/virtual/domain.de/phptmp"
export TMPDIR

# PHP_FCGI_CHILDREN=2
# export PHP_FCGI_CHILDREN

exec /usr/bin/php5-cgi

Some ideas? THX