What picture resolution do I need for Kinko's?

[Zzzt]

I have what I think will be a really good present for my brother and his wife. I'm going to make a collage (sp?) of pics I have of thier new baby boy and various family members. I'll then take the image on disk to Kinko's, and have them print it off on good paper with one of their printers. A couple of these pics are only 640x480. The rest are 1600x1200. At what point does a 640x480 picture look grainy? 3x5? 5x7? I don't know. I don't want to get deep into this, and find out that the final pic looks pixely. Anyone have any experience here?

 

[AkumaBao]

You usually don't notice intil you print a couple 5x7's. The 1200x1600 are great for up to 8x11. Hope that helps.