Frankly, I'm not sure. We've only tested it on 4.x. I'll look into setting up a 3.x test forum. If you decide to give it a try on 3.8.6 and find that it works, please let us know!

how long till ad's show as ive been running for almost 24hours and no ad's showing

VigLink doesn't insert anything into your pages (no ads, no links). We just find unaffiliated links, and affiliate them for you.

I am a VigLink employee as well. We just tested it successfully on 3.6 and up, so you are good to go with 3.8.6.

Installed, don't know if it will make any money but worth a try.

There is no information on how to get paid anywhere though???

From our FAQ:
That policy might change soon (I think we're dropping paper checks and switching to PayPal exclusively), but those are the terms as of today.

Cheers dude, sorry for being ignorant. :)

Is their a way that I can scan the site to see how many links I could convert?

Yup! Submit your site's URL and your email at the bottom of this page (make sure you're logged out, or the form won't be there). There's a fair amount of estimation going on, so don't put too much stake in the dollar figures, but that report will give you an idea of what kind of links you have, and whether we could affiliate any of them.

What is the impact on the forum by adding JS to each page? Would it use up more bandwidth? etc..

There's effectively zero impact on your page load time. The library is downloaded directly from our servers (so the additional bandwidth used is ours), and it's loaded in parallel as your page loads. It won't block the rest of the page from loading as it's being downloaded.