I don't know why you would have to make them so "small" to fit in posts. I post whatever size photo I want in posts because I host them on my own server.
When you pay for a ssnakess.com account, its the same thing. You pay for webspace. Then you link the image into a post using the ssnakess.com webspace address your photo is housed on. It could be as big as you wanted as long as you have that much space in your account. If you are having other resizing troubles, as in qaulity after you resize, that has to do with your photo program or the way you are resizing, not a photo account.