i have one blog that from PR0 to PR3 ...then now PR5 ...i don't involve in building links...what i did is update it frequently
there is no way to know that, your site could jump from PR0 to PR4 or even higher in the next PR update. but keep adding more pages and fresh content and inbound links will for sure help
pr 4 is very easy, now getting a 5 is about 100 times harder, a pr 6 is 1000x times harder, a pr 7 is 10,000 x more expensive all you need for a pr 4 is 1 pr 6 link or a few pr 5 links, so go to wikipedia, and add your link to a pr 6 or 7, problem solved
yes pr 4 is very easy after that it is very dificuly for a 5, 6 , 7 however for a site that is NOT NEW, and has an existing PR, it might be hard because the last few PR updates were mainly for new web sites, and not all old sites were not updated,
I made it!! I can see a nice PR4 in my site. Thank you for your advices, the last update pushed me up to pr4 and almost every subpage pr3. I am very happy, now I will work to make it to PR5 and get to PR3 the other site I own.