The neat part of PHP's built-in XML-RPC is that you basically just build a data structure that matches the kind LJ is expecting, serialize it using the XML-RPC functions, and send it.

It converts between PHP types and XML-RPC types automatically, so it's really, really easy.

One thing you'll find, though, is that it's not possible to post comments remotely. You'll have to send people to the actual entry page.

What? Not Possible to post comments remotely?? Why not? Wouldn't that just be a subset of a post? [Am Talking as if I wrote it, i havent examined the code yet]

::frowns:: I'm sure it could be done, at least in perl, using the LWP::UserAgent mod. Just get something that'll log all requests (iCab for me~ or use a packet sniffer) and look at the POST request, then mimic that. I haven't learned php, but if I recall, there was something similar to LWP::UserAgent... I hacked Pivot a while ago to make it crosspost entries to livejournal. Eh, yeah curl, I believe it was? Lemme try to write up something to post a comment to livejournal using perl, give me a second....

(Gonna be harder to do threaded comments... in that case, you may need to keep a local copy of the comments already posted (so users can see what you're replying to), and then you might as well send users to the livejournal page itself... [/end random side ramble])

Hah! Yep, done~
http://darwin.servehttp.com/livejournal_comment.bml

Current, it only posts anonymously, and only to that entry. Mmm, there's some other restrictions livejournal has worked in. I was able to post a comment the first time without hitting an "Prove you are human" page. Seem's you might be limited to one comment per post per IP per set period of time? Unless you have your users log in. Then there shouldn't be any restrictions, if I recall correctly. There was a discussion about this a while ago, you may want to check

Nevermind that, I searched: http://www.livejournal.com/community/lj_backend/2913.html

So you might have to make a livejournal account that's called "anonymous remote comments" and use that instead, to make sure your users don't hit that sort of problem.

(as for the page I first mentioned... it currently posts to http://www.livejournal.com/users/ibneko/200001.html. The first chunk of code below the form shows the source code of that entry/post-a-comment page(link with ?mode=reply). The second chunk of code is the perl code (html-ified) that powers the page.)

hmmmm... well I guess that would be a solution... what if i had the comment post emulate the lj page comment post? soo the user would find themselves on the official comment page after (unless i played with opening a new window and then closing it...) but then the anonymous post would come from their ip? That would bypass the anonymous rate limit... and it would house the comment setup on my website... of course that is assuming that I can fetch the comments... which i can right?

Emulate... as in grab the lj page, modify some to make it look the way you want, then pass it onto the user? That's actually what I'm doing there... 'cept I'm stripping out practically all of the page, then setting up the form so that it the form sends the users to the official do-comment page (talkpost_do.bml). So: User, request->Your Server
Your Server, get page->LiveJournal
Your Server, parse page, fix, whatever, then send back to->User
User, sends comment in POST talkpost_do.bml request->Livejournal
LiveJournal, sends official Comment Posted page->User

Granted, you _could_ also do:
User, request->Your Server
Your Server, get page->LiveJournal
Your Server, parse page, fix, whatever, then send back to->User
User, sends comment in GET/POST request->Your Server
Your Server, passes comment->LiveJournal
It certainly gives you more control with where the users go... as with the former, users will have to rely on the back button to go back to your site. I think you could probably make an invisible frame that'll bring the users back though? I dunno. May not be a problem if all of your users are techie enough to know they were sent offsite. (as opposed to someone like my mom who would be very lost and confused. XD)

And yes, since each user would have his or her own IP, unless they are posting comments more than once a minute, they won't have problems. Even then, they'll just hit livejournal's prove-that-you-are-a-human page, and that shouldn't pose too much of a problem for most, unless they're both deaf and blind...

And yes, you can fetch the comments. PHP equiv:
$ch = curl_init("http://www.livejournal.com/['users' or 'community']/[username]/[entryid].html");
curl_setopt($ch, CURLOPT_HEADER, 0);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$buffer = curl_exec($ch);
curl_close($ch);

Umm. I assume it's returned in $buffer. I dunno, I've never used php to read site responses.. only done it in perl. I'm sure you can figure it out with a quick google serach though.

People like me have been yelling for this for years. There are a lot of things that can't be done through anything but the web forms -- primarily any access to comments.