So many replies in this thread seem to be confusing page rank with trust rank. There is nothing about a PR0 site that indicates google finds a site untrustworthy. Even if it's still a PR0 after a year, it isn't because it's seen as untrusted.
All that google considers a PR0 site to be is one that not too many people are linking to. Contrary to what some people in this thread might think, that's actually the bulk of all pages on the internet. lol
To a very small extent the fact that even after a year or so a site doesn't have many backlinks, google may consider that as a factor for not increasing trust rank but that isn't the same as some kind of penalty that will decrease it. It certainly isn't going to damage your site if you get a backlink from it if that's the only factor your seeing. If a site has a lot of backlinks, (which can increase it's PR) that might be a positive trust factor for that site, but not having a lot of links isn't seen as a negative trust factor.
The only time I might be concerned about the PR being an indication of trust factors would be in the explanation eldran gave about checking it against the mozrank. I think that would be a lot of trouble to go through for every site you come across though. I think I'd only suggest bothering with that if the site looks like there may be some reason to be concerned. In that case I still probably would just skip that site rather than go into an indepth analysis of it. I think overall it isn't usually a big concern.
The main thing to think about is that PR is determined by the number and quality of backlinks to a site, as such a link from a higher PR site will pass along more link juice, but low PR sites are still good as well. It just takes a lot more low PR backlinks to give the same benefit as a single high PR backlink for indexing your sites position in the serp for any particular keywords. In other words if you're just looking at PR values then all backlinks are definitely not equal, but they are all still good.
Trust Rank though is a completely different matter. A high PR might benefit a sites Trust Rank, but a low PR isn't an indication of low trust. Low Trust Rank (especially of the type mentioned in earlier replies in this thread) is based on things like how many spammy outbound links there are (link farms), and other similar type factors that indicate sites that google considers bad neighborhoods.
So ignore any advice that suggests a backlink from a PR0 page will hurt you're ranking. It won't help as much as a link on a higher PR page, but it will still help. You need a lot more of them to get the same results, but there's no reason to completely avoid them.
edit-
To answer the OP question, for the most part a backlink from a PR0 page is a backlink from a PR0 page regardless of the PR value of the home page. There may be some slight increase in value between a PR0 page on a PR6 site over a PR0 page on a PR0 site, but if there is it isn't likely to be hugely significant. The reason it might have a slight advantage is if there's a link trail from the PR6 main page to the PR0 inner page then there will be some link juice flowing to that inner page. Probably a little more than what is flowing to the inner page of the PR0 site.
The thing to remember is that the PR value of a page is just an indicator of the link juice flowing to that page. Google doesn't actually use the PR value itself, the algorithms are keeping track of the actual flow. What that means is that sites with equal value PR don't necessarily have the same amount of link juice. What the number gives us though is a range. So a backlink on one PR2 site may be better than a link on another PR2 site, but no matter what, any PR2 site will have more link juice than a PR1 site, and less than a PR3 site. Also the amount of link juice you get from a page is also dependent on how many outbound links that site has. A backlink from a PR1 site with only a single outbound link may pass more value to your page than a backlink on a PR2 site with 50+ outbound links. Also remember that the actual PR factors the algorithms use is a constantly adjusted, so the longer it's been since the last PR update the less reliable the PR number you're seeing actually will be.
