Hi, everybody!
I do have a website with PR 4,
MagicTemplate.com. To speak a bit about this: the PR reflects the quantity and the quality of the sites linking back to you. The more sites link back to you, the better and you get a higher PR. So in order to get a PR of 4, you should get some links. I can not tell you how many since there is not a fix number. Here comes the quality of the links. If you have hundreds and thousands of sites linking to you with a PR 1, you will not get that PR 4 you want. But If you have a few sites with PR 4, 5, 6, etc linking to you, then you might just get that PR 4 you like. By the way, it is not that hard to obtain a PR 4.
Coming back to the question, how did I get it? My site I mentioned above distributes free Christian site templates, for download. Each of the template has a link back to my site so each site using one of my templates will keep such a link to my sites. There are quite many sites using my templates.
This is the way.
Since you don't distribute such templates, you should put a link in the bottom of the posts on such forums, in the signature, comment on blogs, a lot, I mean. Trade links with fellow webmasters, etc.
Hope that helped you!