Recen project we were working on needed some forms to be posted to certain services. Knowing that SharePoint's pages are one big form and you can't nest another form inside another this starts becoming a problem.
But I remembered a while ago I was watching how the guys over at MSN spaces did it with the "Blog this" functionality. So based on this I've made similar script and methodology so you can create "forms" that make POST or GET from within SharePoint's Pages. The script is not fully automated, since it directly works only in IE, but with minor additions specific to your form, you can get it working easily in other browsers also.