Bagi,
Its good to have vBSEO but from my experience it has not really brought any additional traffic etc.
You can hack vB to make it SEO friendly BUT you will have LOOOOTS of work to do in future because some of you mod rewrite hack will not be compatible with some of the future vB updates (this is one of the advantags of vBSEO they do all the programming at each vB update releases)

Thank you Temi for the fast answer! Would you be so kind to tell me how often do they release new vBulletin updates?

Minor updates sometime twice in one month, major updates probably every 3 months or so, this is a very rough estimate.

Use SMF and be damned with it

Bagi,
This software is very search engine friendly: MyBB - Home , you can have a look at it in action here: International Forum Awards (IFA) - Forum of the Month look at the threads and topics, all clean urls.

I have never used it before but If I am setting up a forum I will be using it.

Well, if you're a do-it yourself kind of guy take a look here:
The quick 'n' dirty ultra simple vBulletin SEO hack - Existing Scripts

I will strongly advice anyone against that, even Dani the creator of the hack does not use it any more, she bough vBSEO.

I used that have for this forum a few years back, it does work but IS A BLOODY pain each time vB update that conflicts with it is released, I also used it on Ozami actually but same problem, not a good idea if you are a forward planning person

I agree on that. I just gave it as an example of what can be done.
But that implies that you do it everytime there's an upgrade and also, you'll need to modify the code eventually.
vBSEO does it all for you (and more). Main problem is you need to buy it.
But it does its job well.

Guys, thank you for the answers I have just recognised them. With my Partner in this forum project want to install something respectable script, which will deter the competitors. Nowadays at the hungarian net there are some SMF and PHPBB and one invasion webmaster forums, so we still have the opportunity to maintain the WEBMASTER FORUM. Now I'm sure that it have to be the vBulletin, and I won't be able to go without vbseo, though I'm one of those "do-it yourself kind of guys"