Do links from sites with bad rank help or hurt?

If I want a page rank of 7 should I even bother getting links from sites with a page rank of 2 or 3?

You should be getting those links if those pages/sites are relevant to yours if you care about your ranking. IF not, do not even think of selling page rank or else you Google will be hunting you down.

Thank you for your reply but I am still confused: do links from sites with poor page rank help or hurt me or neither?

Pages from sites that are related to your site's industry or topic always help. In general, any link you get is either helpful or doesn't hurt. Links to your site cannot hurt your rank, because if they did, then that would let your competitors build hurtful links to your site and derank your pages. The only kind of links that can hurt you are the ones you control - the outbound links on your site - so try to avoid linking to warez/spam/porn and you'll be fine.

Relevant Links are always helpful no matter they have high or low PR... Its known that High PR links are always best for quick PR and search results. Unlikewise, low PR links take some time but show great results timely.
Also, it is difficult to get high PR links easily but not in the case when u r going for low PR links.

Backlinks from PR 2 or 3 aren't bad. They are always countable. The difference is only PR 5 link is better than PR 2 link. But PR 2 link is not a bad one until it is relevant.
You want to go to PR 7, You can not get PR 5 or 6 each time. You have to get links with some PRs more than 1 . Finally all PR links are useful.
But PR 2 link is far far better than PR 5 link from a bad(banned/porn) site.

Relevency is more important.you can get link from anywhere but site should be relevent to your site.

when u r talking about relevancy then what "link from anywhere" makes sense???

Links from relevant sites are always appreciated whether they have PR High or Low. High PR links are difficult to gain, it needs time but in that time u can gain more Low PR links..
which is always beneficial 4 u???

All (followed) links help, some more than others, but they all help.

Assuming equal relevance - a high PR link is generally considered to be more valuable than a lower PR link (but... they ALL help)!

A link from a porn site will NOT hurt you and (assuming equal relevance) I would far rather have a link from a PR5 porn site than a PR2 general site.

Just be patient with it. Improve on your content for the mean time.

As Clicky B pointed out - all links (that pass on PR) help.

don't pay too much attention to the green PR bar, all links with no "nofollow" tag are relevant. In fact, even links with rel="nofollow" is good as long as it gives your site traffic

You need quality and quantity. So take what you can get.

An exception would be if the site got punished, dont get a link there as it could be "bad neighborhood".

Even if we get relevant sites with lower pr linking to us, should we try to only link to those websites that have equal or higher or does that not matter as much? As long as they are relevant of course.

But a link FROM there will still not hurt you! You should just avoid linking TO there.

When it comes to linking out, PR of the linked site is entirely immaterial.
Just be sure it's not a "bad neighbourhood site" (if it's cached & indexed by Google it's most likely fine).

Linking to the website having a page rank of 2 or 3 will not hurt you. It depends on the contents of the website. If you link to the website having similar contents then it will sure help you to increate the impressions you will get from the inbound links.