Can you make my idea a reality?

[DSLR noob]

Ok I have photoshop CS2 and I took a few photos during a weekend yearbook thing and an idea to fuse 2 of them struck me. I really wanted this one picture of a Coke can (I hope you'll recognize which one) to look really exxagerated in size when I took it, only when I looked in the LCD, did I notice the 1.8 aperture made the light on the cieling look like a sun/moon. A picture I took later that night is a small handheld city scape picture from my hotel room at ISO 1600. I decided it would be cool to put the coke can as a huge towering mass above this city and add some shadowing. I also wanted to render some whispy clouds in the background, a few overlapping the can, and one overlapping the "moon" maybe with a few stars but mostly black sky.

Well turns out I could render clouds, bu tI am bad at layer masking and belnding and I couldn't get the effect I wanted so I just left out clouds all together. I also did the shadowing wrong, and I probably should have the bottom of the can layered behind the city rather than floating 300 feet (if going by scale) above the city, but I couldn't get it behind the lights. Basically, can anyone make my idea look like I wanted (a sort of ad-like convincing giant Coke picture). Please tell me (as detailed as possible) what you did as I am asking you to do this not for an easy way out, but to learn and improve.

Ok so here are the pictures:

And here is my failed atempt:

 

[glaston]

Well, what you're talking about isn't really as hard as you think.

That being said, what you want to do is start all over.

The biggest problem is that the 2 images you have here aren't suited to be comp'd in this way.
Their perspectives are completely different.
The image of the coke can is taken at an upward angle, while the scene image is from a slightly downward angle or elevated position.
You want both images to have matching perspective.
If they were, the attempt you made wouldn't be so dissapointing to you.
As it is, in reality, the coke can tower would be leaning away from the camera.

One mistake I think you're making is focusing on the light sphere in the coke can image. You can recreate that aspect without using the actual light from the coke can image.
Adding a moon once the images are layered and aligned would be the ideal way to go.
The attempt you made serves as a photo sketch to lay down the concept idea (like a storyboard of sorts). Now you need to get the shots needed to realize the end product.
I could easily do what you're asking within reason. By that I mean I could lay the ground work then you can detail to your hearts content.
But to realize your exact idea would be more work than someone would want to put into something that isn't their own, or that they aren't getting paid for.
Beside that, it would be much more beneficial to you to have someone advise you on it rather than do it for you.
Also, the above images really aren't high enough in resolution to do anything with. They're compressed and downsized for the web.
I would need the original image files that are hopefully large enough to provide enough data to work with (RAW would be ideal but psd or tiff files with decent resolution will do also).

Before going any further, you'll need to re-shoot the coke can and match its perspective to the scene image (or at least as close as possible).
If you get the new shot, I can do the basics and then pass off the .psd file to you so you can add detail and refine it to your liking.
Don't resize, resample, or convert to a different format. Post or send me the files as they are when you pull them into the computer.
All I will do is separate the image into layers to get the coke can positioned, and position the foreground and background elements the way you want them to appear, and advise you on blending and layer style.
The detailing is all you
I know you said you aren't that great with masking and blending. But if you want to do compositions like this you'll have to change that. And the best way to learn is to delve into a project that is just outside your skill level.

Regardless of how you want to proceed (let me help you or give it another try yourself), you'll need to re-shoot the coke can with a matching perspective.
That's inescapable.