I've enabled mod_cache, mod_expires, mod_headers modules during my httpd.conf as well as added following text

 ExpiresActive On

<ifModule mod_deflate.c>
  <filesMatch "\.(css|js|x?html?|php)$">
    SetOutputFilter DEFLATE

<ifModule mod_expires.c>
  ExpiresActive On
  ExpiresDefault "access plus 1 seconds"
  ExpiresByType image/x-icon "access plus 2592000 seconds"
  ExpiresByType image/jpeg "access plus 2592000 seconds"
  ExpiresByType image/png "access plus 2592000 seconds"
  ExpiresByType image/gif "access plus 2592000 seconds"
  ExpiresByType application/x-shockwave-flash "access plus 2592000 seconds"
  ExpiresByType text/css "access plus 604800 seconds"
  ExpiresByType text/javascript "access plus 216000 seconds"
  ExpiresByType application/javascript "access plus 216000 seconds"
  ExpiresByType application/x-javascript "access plus 216000 seconds"
  ExpiresByType text/html "access plus 600 seconds"
  ExpiresByType application/xhtml+xml "access plus 600 seconds"

<ifModule mod_headers.c>
  <filesMatch "\.(ico|jpe?g|png|gif|swf)$">
    Header set Cache-Control "max-age=2592000, public"
  <filesMatch "\.(css)$">
    Header set Cache-Control "max-age=604800, public"
  <filesMatch "\.(js)$">
    Header set Cache-Control "max-age=216000, public"
  <filesMatch "\.(x?html?|php)$">
    Header set Cache-Control "max-age=600, public"

<ifModule mod_headers.c>
  Header unset ETag
FileETag None

<ifModule mod_headers.c>
  Header unset Last-Modifiedd

<IfModule mod_cache.c>

LoadModule mem_cache_module modules/mod_mem_cache.so
<IfModule mod_mem_cache.c>
CacheEnable mem /
MCacheSize 4096
MCacheMaxObjectCount 100
MCacheMinObjectSize 1
MCacheMaxObjectSize 2048

but files aren't caching. I recieve headers information like

Date    Tue, 23 Aug 2011 11:30:09 GMT
Server  Apache/2.2.19 (Win32) PHP/5.3.6
Last-Modified   Mon, 22 Aug 2011 21:24:19 GMT
Accept-Ranges   bytes
Cache-Control   max-age=216000, public
Expires Thu, 25 Aug 2011 23:30:09 GMT
Vary    Accept-Encoding
Content-Encoding    gzip
Content-Length  2875
Keep-Alive  timeout=5, max=100
Connection  Keep-Alive
Content-Type    application/javascript

Request Headers

Host    workflowsf.com
User-Agent  Mozilla/5.0 (Windows NT 6.1; rv:2.0.1) Gecko/20100101 Firefox/4.0.1
Accept  */*
Accept-Language en-us,en;q=0.5
Accept-Encoding gzip, deflate
Accept-Charset  ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive  115
Connection  keep-alive

Have u any idea where I'm wrong? Thanks ahead of time

That appears just like a fairly good config. You've got a typo together with your Header unset Last-Modifiedd and you also most likely have no need for the very first line because it is a replica from the line inside <ifModule mod_expires.c> which is really a better place for this.