I am rendering some pictures in poser 7 to be printed up on posters and canvas and such. Should i change the dpi in poser to 300 dpi, or is it ok to render lower then make it 300DPI in photoshop?

Not an expert, but I would think you would loose detail if you did the latter. I would render at the highest setting. But then that is just me.

Unless something changed since P6, DPI in the render makes absolutely no difference at all to the render quality.  You may as well render at the default setting but make sure the render size is big enough to print at a decent size in 300 dpi. 

if you want 10x8 at 300 dpi (for example) then you'd render at 3000 x 2400 pixels and set the DPI in photoshop

dpi is dots per inch. 300dpi is about standard for printers. There's tricks to send this higher.
Unless things have changed, resolution on most monitors is 72 ppi (pixels per inch),  I wouldn't be surprised if this is no longer true, though.

I remember seeing a tutorial somewhere about pixel settings vs image sizes. Or maybe it was just a thread. You might drop a line in the Printers forum, they do a lot more of the high-end printing and know this stuff better than I do.

Use pixels and reset in photoshop so your image sizes properly. 

Bottom line: DPI doesn't exist on your monitor. For print, you render in pixels by calculating total size x 300.

In Render Proportions on Poser Pro, I set my dpi to 1000 just to be on the safe side, not so much for printing, but for adjusting the scale if necessary in Photoshop.  This way, even if I scale the render to twice its size, there isn't the pixelization that would normally occur.
dph

Myth. Pixels are pixels, and renders are not vectors. Number of pixels is the only thing that matters until you get it to a print prep application.

What Believable3D said.

It's really simple, we need two pieces of information:

a) the physical dimensions of the printed output
b) the number dots / pixels per inch required to produce good quality results

Let's say your print size is 12 inches x 16 inches: if your print shop wants the image at 300 dpi, you will need to make the image (12 x 300) x (16 x 300) pixels. That's 3600 x 4800 pixels.

There are a lot of reasons why you may not need the image to have as many as 300 dpi, but printers and designers are lazy and 300 dpi is safe.

If you want a rambling, long-winded discussion about any of this click on the top link in my sig.

ok and to set my pixels in poser i just re-size the image dementions?

Poser does the hard work for you.

On the left I've chosen Inches for width and height (you have to change both, and uncheck constrain aspect ratio) and entered 16 and 12 respectively and 300 pixels / in as my required resolution, then clicked OK.

Then - on the right - I opened the render dimensions dialogue again and, as you can see, the correct number of pixels have been calculated.

Quote - If you want a rambling, long-winded discussion about any of this click on the top link in my sig.

Thank you so much for this article. The folks that can explain the difference between DPI, LPI and PPI are unfortunately very rare these days. Now, if we can next tackle and eliminate the "screens are 72dpi" myth...

Xactly.

My laptop is 1920x1280 with 15.4 inch diagonal. resulting in about 150 PPI.

My desktop is 1920x1280 with 26 inch diagonal, resulting in 89 PPI.

To just say that screen PPI is "some fixed number" is like saying a piece of string is 3 inches long. In other words, some are, some aren't. (Hi Noel - how long is your string? LOL)

Pixels per inch is a ratio where you divide the pixels by the inches. Since both can vary, it is meaningless to suggest that all screens have the same PPI, even for laptops.