Deriving part not working

[anthtroupe45]

I am new extremely new to Inventor and I cant figure out how to create a scaled down version of a surface model of a car have I download. As of now it is just a bunch of composite surfaces. I tried to derive the car and scale it but it didn't work. I figured out that it needs to be a solid and tried to convert it to one using the stitch command but i keep getting an error saying that no meaningful result could be made. I just need help figuring out what to do. 

Thanks.

[JDMather]

Surfaces can be derived as well as solids.

Zip and attach your original file (or url to download) here.

[anthtroupe45]

http://www.mediafire.com/download/nicg6zj6kvjeaka/SMART_FINAL.ipt

[anthtroupe45]

I hate to bug you but i was wondering if you were able to figure out what was wrong.

[JDMather]

I don't go to third party file sharing websites that put garbage on my machine during the download.

Attach the file here or at Autodesk360

Find the red End of Part marker in the browser.
(End of Folded on sheet metal parts EOF)
Drag the red EOP to the top of the browser hiding all features.

Save the file with the EOP in a rolled up state.

Right click on the file name and select Send to Compressed (zipped) Folder.

Attach the resulting *.zip file here.

[anthtroupe45]

http://a360.co/1dSzxfD It was too large even when in .zip so i used autodesk360

[anthtroupe45]

I feel like I keep pestering you, but I really need the help. Did I post the part on Autodesk360 correctly?

[JDMather]

What is the source of the original file?  Do you have the url to the original file?

(looks like it was an stl file to me)

What is the end purpose (stl files are generally of little use in an engineering program).

I had no trouble deriving the surfaces - post screen shots of where it is not working for you.

[anthtroupe45]

My overall goal is to CNC a block of bass wood into a model of the car. The car is CO2 powered and has certain limitations so i need to create axel holes, a hole for a CO2 cartridge, and make the mirrors removeable. I was just trying to do this in inventor (because its the only software I have downloaded and know how to use), and then Im  planning on exporting it into a file type that the CNC can use.

This is where i orginially got the file http://www.3dcadbrowser.com/download.aspx?3dmodel=6321 I chose to download it into a .dxf because I thought that was the only one that would work good.

When i was deriving it, it wasnt showing up. Only certain areas that i was able to stitch were (i kept getting an error that i wasnt able to solve for the other areas). What i needed was everything to show up, not just the stitched surfaces. I would post screenshots but my computer is extremely slow. 

Im contemplating not putting the modifications i listed erly into the part file, if it wouldnt work or be too hard and then just drilling them into the wood after the car is created.