TO gain high PR u need to do proper link building of your website....you may use traditional ways like you may do directory submission, article submission, social bookmarking.....social bookmarking will also help you 2 gain huge traffic and that may even giv u few loyal customers for ur car rental business directly. You may also use blog reviews and blog commenting as it helps to gain PR.....this procedure may take long....and if done very fast may harm your site...hence you need 2 make a appropriate strategy for it.... If you need to gain huge traffic and high PR, I can give you a hand......if interested PM me
To get High PR you can do directory submissions on High PR Directories. Also Write some good articles explaining about your car company and services provided by it.
you need to concentrate more on off page optimization over the time with maintaining natural speed of submission like Directory,Article,Bookmarking and many more..but dont spam.