Image editing

Hello All.

I want to write an application that does the following.

1)Upload an image from browser,
2)Resize the image to 300 x N
3)Save the image to a database table or file system.
4)Create a thumbnail of that image sized to 75 x N
5) Save the thumbnail to a database table or file system.

I have all mechanics of the database table or file structure down as well as the uploading of the file. I am not sure how to do the image editing part however. I am assuming after some research that the GD library is what I want to use. Is that correct? Or do I have to write an interface to GIMP? That wont work, because although I am developing on Linux its gonna end up on a Windows server.

Can I install GD after PHP has been installed?

Thanks for any advice on how to accomplish this task.