Link to the Form
Create a normal hyperlink in your web page or email and add the link URL as:
http://www.yoursite.com/machform/index.php?form_id=28
TO add this as a hyperlink to a web page, copy and paste the Embed Code (Basic link) to the "code view" (or HTML View) of your web page (if using an editor like Expression Web or Frontpage).
The full basic link code would be something like this:
<a href="http://www.yoursite.com/machform/index.php?form_id=27">Click here to view form</a>
You've said in your original question the link is broken, but it sounds like you're trying to copy the wrong address into the browser address bar or something - make sure you only copy (or type in) the full address:
http://www.yoursite.com/machform/index.php?form_id=28
Adding Logo to the Form
Putting a logo on the form is easy enough - all you need to do is add the HTML code for an image, as follows:
<img src="http://www.yoursite.com/images/your_logo.gif">
Add this to the "Form Title" section when you edit the form.
There's nothing in Machform limiting the type of image you can use, this is generally limited by the types of images used on the web - PNG, GIF and JPEG.
Size of file is not limited by Machform - rule of thumb for web design applies here - image files need to be the minimal size possible - balance between quality and file size (in terms of kilobytes, not dimensions).
If the logo comprises of a photo or full colour image, use PNG or JPEG, if it has limited colour (up to 256 which is not suitable for photos) use GIF format.
Other than that there's no limitation in respect of images you can use.