I looked into a built in spell checker for the forum and installed one, however it was not function properly...more so it was pretty whimpy in comparison to what google offers. Below is a Tool bar which install into your web browser, one is for Fire Fox and the other is Internet explorer. I highly recommend you download and install it if you are a bad speller
Once installed you simply click on the "ABC Check" at the top of your browser. To stop spell checker simply click on "Stop"
Fire Fox Browser http://pack.google.com/intl/en/product_info.html?ff Microsoft Internet Explorer http://pack.google.com/intl/en/product_info.html?tb