Placing a .jpg in Illustrator

[#1]

When I create an .ai doc that has specifiic dimensions of say, 300pxw x 250pxh and I create a jpg in psd with the same dimensions @ say 150dpi, why does in come in smaller not filling the space of the dimensons in .ai?  

We want the best detail of the image, not pixelated as we're getting.

It must be a resolution issue.  In .i I can only setup a pel sized file at 300, 150, 72 and 36dpi.

So if I set my file at 150dpi, 300px X 250px, and my psd file is the same res and. dimensions, why then dopes it drop in much smaller and pixelated? 

[#2]

When I create an .ai doc that has specifiic dimensions of say, 300pxw x 250pxh and I create a jpg in psd with the same dimensions @ say 150dpi, why does in come in smaller not filling the space of the dimensons in .ai?  

We want the best detail of the image, not pixelated as we're getting.

It must be a resolution issue.  In .i I can only setup a pel sized file at 300, 150, 72 and 36dpi.

So if I set my file at 150dpi, 300px X 250px, and my psd file is the same res and. dimensions, why then dopes it drop in much smaller and pixelated? 

[#3]

You can't set a document PPI in Illustrator, only a real physical size that corresponds to 72 PPI.

A 300 x 250 px document in Illustrator is 106 x 88 mm.

A 300 x 250 px image at 150 PPI is 51 x 42 mm. That's the size you'll see in Illustrator.

The 150 PPI image has not 'lost' any pixels/resolution, it is just displayed at the physical size it is relative to the Illustrator file.

Talk us through exactly what you want to achieve and we can advise.