You're welcome to try posting it as a .zip, however there are a couple of problems with that.

First, un-zipping the file requires PKzip, a utility that is outside the standard Windows operation system. That's no big deal because it can be downloaded for free off the net. But posting a cleaned up (properly compressed) .jpg is easier and guarantees universal compatability for your intended viewers.

For many people however, including me, there is a much bigger problem.
A .jpg file is a benign file that simply opens up and sits there.
However, a .zip file MAY contain malicious code in the form of any number of viruses that can wreak havoc on the downloaders/openers system. It is easy to bury intentionally nasty executable files within a .zip that are unleashed when a file is unzipped.

Understand that I'm certainly NOT accusing you of intending any such mischief.
HOWEVER, using .zip files to cause harm is one of the most common ways that those who DO mean to cause damage use to spread their bad idea of a sense of humor.

It is for that reason that I won't open ANY .zip file unless I PERSONALLY know the person who actually zipped the file, and exactly what's in the zip file. I won't even open a .zip that someone I know has passed on to me but that was originally passed to him from someone I don't know.
I don't think twice; I delete them without opening them and just about everybody who has been bitten by a virus of one kind or another has learned their lesson and does the same (if they're smart).
I doubt if very many people would have the courage to open your posted .zip file which would defeat the purpose of why you are posting it.

I suggest you stay with posting a .jpg. Any of the photo editing programs (Photoshop, et.al.) are capable of resizing a photo and compressing it so it is a managable size for uploading/downloading off the net, even with a 56k connection.
Since you're only attempting to show others what your design looks like (and not to give them a CAD file for editing themselves), your best bet is to print it out and then scan it so you can post it as a .jpg.
Alternatively, perhaps there is some kind of image file that your CAD program can export to?

Highflight