Ok, I'm about to redirect my old site design www.domain.com to a wordpress blog www.domain.com/wordpress using a permanent redirect. If I keep getting new links to just www.domain.com will it continue passing pagerank to /wordpress forever?
Yes, but you want to start aiming them towards the new domain name after you start the 301 redirect, it's rather silly to keep pushing links to a domain name your no longer using.
Yeah but it's easier to market the domain not the subdirectory and some directories require only the domain. I just need to be reassured that it won't make a difference to page rank if I continue to get links to the domain it will be fine.
You will be fine, in normal situations it's best to get links to the actual URL but plenty of big companies do redirects like you want to. www.microsoft.com for example, mostly it's for a good reason such as geo content delivery. May i ask why you would want to ditch the primary domain and go with a subfolder?
Because I'm switching to wordpress but want to redirect all of the old sites pages to the new wordpress ones.