hi i just wanna know this thing.. assume that i have a website www.mydomain.com with PR 0. now i create a number of subdomains like sd1.mydomain.com,sd2.mydomain.com,sd3.mydomain.com etc. now if i place my main domain's link on my sub domains,will it help my main domain to get a PR
Links with no PR cannot pass any PR. Your sub-domains would have to have links from other sites that pass PR to them before they had the ability to pass any PR. Just creating a bunch of sub-domains and linking them to the main domain will not do anything.
Sorry Cupid, as your sub-domain pages do not have PR, hence they would not be able to pass any PR to your Homepage. Should your sub-domain pages gain PR from somewhere, they might be able to pass some percentage of PR to your Homepage.