How do I cut images then enlarge and transfer to another image on GIMP?

[mahesh]

I am attempting to cut a piece of an image from a photo then enlarge it then transfer it to another photo and I am wondering how to do this. I have attempted the Alpha Channel and Mask stuff but that's not working for the image will be several times larger than it is on the screen and either with a white background or it will be completely see-through. Any real assistance would be greatly appreciated. Thanks.