Buying links is definately ok, as long as they look natural. Like contextual link purchases, for instance. I am new at the whole SEO thing and did all the wrong things. I purchased site wide, links stacked on top of one anther, non-relevant links, high PR links, THEN read what was supposed to be done. I am now a repentant back-linker!
Having done all the wrong things, my search engine positioning is still ok. So, the supposed penalties that get tossed around in the various forums are overly hyped.
I am not sure about forum etiquette (so delete this link if not allowed!), and referring other forum threads, but here is one regarding link purchases:
http://www.highrankings.com/forum/in...opic=28298&hl=
Also, here is a very good read on natural link building. Probably one of the best summations if found:
http://www.jimwestergren.com/link-building-guide/