Well I don't know how helpful this will be. I don't have the program in front of me so I'm going to do this all by memory. Lets say you want your final out put to be 6in x 4in at 400 dpi. For the best quality, export your Allustrator file at 600 DPI.
Open your exported AI File in Photoshop. The create a new document at 6in x 4in at 400 DPI. In the exported AI file, Select all and drag the AI image to the New Document.
What will happen is that your image will be to big for the view. This is okay. If my memory is right you can go to Edit, tranform, Scale. Then if you hold in the Shift KEY while Scaling the art work it will hold the same proportions.
When you get it to the size you want, simple hit enter and it will apply the anti alise thing it does. Smooths out any kind of rough edges usually.
What you should see is how you will want your file to be printed. This method has worked for me before with no problmems.
5656, you asked how do you resize in photoshop. If my memory is correct, I think there is a menu option for Image, or not, I can't remember, You can resize the w and h. But doing so can works, but can pixilate easily.
Like I said, I haven't worked in AI or PS in a while. SO i'm doing most of this out of memory. I hope that some of the stuff I've said might help.