Can anybody suggest the best software to use for developing an e-ccomerce site on my mac:?:

Perhaps try eOrdering by LAJ Design? It's available for both PC and Mac (universal binary), and costs $75 for Gold (or $450 for Professional). It also offers a fully-functional trial for a period of 20 days.

Actually there is a MAC-style (cool looking, fast loading, apple-style storefront, etc. etc.) service available; which is NOT limited to MAC per say AND it is online. Plus, there is absolutely NO coding required!!!

I think that is cool because you could make your storefront from anywhere on anything as long as you have internet! Check it out, it's called SHOPIFY ... checkout their showcase (examples); basically delivers & makes your storefront look very professional, period. This makes Zen-Cart looks like sh|t, LOL Enjoy! ;)