So i'm working with these picstures...some are high [300ppi]res some are not [72ppi..]

and i want to crop them so that when I import into avid it wouldn't be distorted etc...

I am working in photoshop and i set my crop size to 640 px/480px and when i crop the picture gets REALLY REALLY pixelated..

is this the correct aspect ratio for native ntsc SD. I do believe it is...is there another method that I can adopt so that my pictures 

wouldn't become pixelated?

Any help would be appreciated...

Resolution should be 720x486 for NTSC. I would also look at using the Avid Pan and zoom to bring in the Hi Rez images.

 Yes, pan and zoom is definitely the way to go here, because you won't have to re-size your hi rez image. Just park it on your system drive, and instead of creating an Avid media file as in a traditional import, the system will point to that file directly and allow truly resolution independent moves. Keep in mind this image must remain on the platform for the duration of the project, even after the effect is rendered. Also, if you move the project to another platform, you must move the hi rez file as well, and define a new path to it on the new platform when opening the timeline containing the P & Z effect. I place a "P & Z" folder on my desktop for that purpose.

thnks ...

but i am familiar with the pan and zoom...

whats i was attempting to do is create alpha channels with the images in photoshop so i can do some different stuff with them in 

avid. So i was going to resize, create the alpha channel for the selected images then import them both into Avid...

thats why i wanted to resize them in photoshop first..

any thoughts??

 Then first of all, as pointed out, native aspect ratio for NTSC SD is 720 x 486, 720 x 480 if DV.

Create an associated alpha channel with the image in Photoshop and size as desired, and when importing to Avid use the following options: Aspect ratio: Maintain size. This will import the image non-distorted. Color levels - RGB. File field order non-interlaced. Alpha channel - invert. This will create a matte key clip, but it will not be resolution independent on moves. The only way to do resolution independent moves is Pan and Zoom.

I'm not at my Avid right now to test, but if P & Z will allow a matte key to be nested on top, you could create a cookie cutter (white on black) of the alpha and mate it to the appropriate fill image with a pan and zoom applied. Both P & Z movement and matte key movement parameters would have to match.

No-one else going to say it?  Oh, well, here goes...

The dpi settings of your files only apply for print media.  As the guys have said, the only thing that Avid or any NLE cares about are the total pixel dimensions of the image.  You will see references to 72 dpi as video resolution - well, it's not.  It's just a convenient figure adopted in the early days of computers when a 17" monitor was considered big, and it wasn't an accurate figure even then.

In brief, what the dpi setting in Photoshop does is change the on screen size at which an image will be regarded by Photoshop as being at 100% magnification.  If you magnify a 300 dpi 720x486 image to the same on-screen size as a 72 dpi one it will tell you that the 300 dpi image is 417% magnification while the 72 dpi one is 100%.  Imported into Avid, both will be exactly the same.

For working convenience you can change the dpi settings of your 300 dpi images in Photoshop to be 72 dpi, as long as you don't resample.