If you can't naturally obtain em, buy em. Ensure that your links are from relevant clean sites. And do not leave an obvious trail.
no way google would ban u for a text link, as gr8liverpoolfan said it has to be from sites which have content similar to your website example : business site would need links from other business related websites, links from joke site to biz site would be meaningless
Buying links still works as a way to increase PR - but when you cancel the links, you lose the PR your site gains, so it's always better to get permanent links of some form. Submit a few articles to some high PR article directories, get some links from some of the more respected social bookmarking sites. It's not that difficult if you formulate a plan and stick to it. Cat'
Google does not recommend however to buy links, however they won't ban you for this. Read Google webmasters recommendations in www.google.com/webmasters