I finally figured out that the tables weren't causing a problem in my HTML e-mail. (I had to use tables, because I couldn't use DIV and CSS for safety issues with HTML e-mails, and I also had problems with iFrames.)
So, the problem was that when I was pasting the HTML code, there were extra <br> being inserted, ...but it took days and hours to figure it out, because when I was pasting the code I was seeing the code that I was pasting. The <br> were invisible.
See, Dreamweaver moves and aligns my code to look neat. The problem is when I copy the code and paste it into the Compose Message Field of Gmail, Yahoo, and Hypermart.net, all of their e-mail editors took the blank spaces of Dreamweaver's code as <BR>. ..but didn't show up as I was pasting the code. That's like eating vegetables, then you get very sick, the surgeon operates on you and says "we pulled one too many rotten-ed hamburgers from you." ...But you didn't eat them?!
Hotmail wasn't doing that problem, but I had to specifically use Hypermart for the HTML e-mail, so I had to figure out how it works there.
So finally, I pasted the code in Simple Text, got rid off all the blank spaces, so the whole thing looked like a concrete wall and then copied and pasted that code in the Signature Field of Hypermart's Compose message settings (that was the only way to do it).
By the way, does anyone know of a similar editor to Simple Text that's free and it can strip away the blank spaces between lines of text automatically, so that one doesn't have to click the back space hundred times?