The destination of the inbound links doesn't really matter as long as SE spiders can reach your forum from that page. Usually, inbound links point to your homepage and obviously it is beneficial to have links from there to your forums! ;)
It may take some time for your site to get fully spidered and for the pages to be listed in Google.
For example, if you don't have many inbound links, it could just be that spiders haven't found you yet in their regular crawl.
When getting a new site indexed it's advantageous to get inbound links from sites that are indexed fairly regularly. Try registering on a few forums and including your link in your signature (of course, don't spam and only include a sig if the forum allows it! :)).
As long as you have plenty of inbound links from different sources and your site has a spider friendly link structure (ie not too many links on each page, and each page can be reached within a few clicks) then it's just a waiting game - there's not a lot more you can do.
I'd recommend that you keep working on the inbound links to promote spidering. Most people will link to your site's home page, but see if you can get some links to your forum home page or even a category page or two. The amount and quality of linkage have a major bearing on spidering frequency and depth.