Sub vcl_recv | Magento + Varnish

I would like to kindly ask someone for help.
I browsed a lot of pages containing Varnish tutorials and sample VCL files,
but I can't find anything related to configurating Varnish for Magento (at least they don't function right).

All manuals I've found thrown a lot of errors during Varnish starting
and it seems thay are suitable for old versions. (Also none of magento modules
PageCache & Varnish Extension don't work for me, because I think Varnish
itself is not working right)

My problem:

1. I get Varnish to cache front-end, but it breaks almost every
functionalities of my forms, payment module, newsletter subscription, etc., etc.

2. I've found out that changing one word in "sub vcl_recv" changes everything
The word is: return(lookup). This is the code of my "sub vcl_recv":

sub vcl_recv {

if (req.http.x-forwarded-for) {
    set req.http.X-Forwarded-For =
    req.http.X-Forwarded-For + ", " + client.ip;
} else {
    set req.http.X-Forwarded-For = client.ip;        
    if(server.ip ~ a168_144_38_181){
    set req.backend = b168_144_38_181;
    }
}
if (req.url ~ "^/images") {
    unset req.http.cookie;
} 
    if (req.url ~ "^(/index.php)?/(admin|customer|checkout|add|product_compare|switch|___store|referer|contact|chat|payone|sendfriend|review|api|NOCACHE|post|robots.txt|j2tajaxcheckout|cron.php|varnish)") {
    return(pass);
}
if (req.url ~ "\.(png|gif|jpg|swf|css|js)$") {
 set req.http.user-agent = "Mozilla";
 unset req.http.Https;
 unset req.http.cookie;
 return (lookup);
}
   if (req.request != "GET" &&
   req.request != "HEAD" &&
   req.request != "PUT" &&
   req.request != "POST" &&
   req.request != "TRACE" &&
   req.request != "OPTIONS" &&
   req.request != "DELETE") {
     /* Non-RFC2616 or CONNECT which is weird. */
     return (pipe);
}
#parse accept encoding rulesets to normalize
if (req.http.Accept-Encoding) {
    if (req.url ~ "\.(jpg|png|gif|gz|tgz|bz2|tbz|mp3|ogg)$") {
      # no need of compression
      remove req.http.Accept-Encoding;
    } elsif  (req.http.Accept-Encoding ~ "gzip") {
        set req.http.Accept-Encoding = "gzip";
    } elsif (req.http.Accept-Encoding ~ "deflate") {
        set req.http.Accept-Encoding = "deflate";
} else {
# unknown algorithm
remove req.http.Accept-Encoding;

remove req.http.Cookie;
remove req.http.X-Pass;
set req.grace = 30s;    

return (lookup);
}
}

Can someone kindly help me with setting this up?

Any help would be greatly appreciated!!!

Thank you. Thomas