The NATATA Anti-Spam Encoder is a simple to use utility that allows the Web developer to easily turn plain-text Web mailto hyperlinks into hyperlinks that appear perfectly normal to the end user when viewed on a Web browser. In terms of the page's HTML code, they show as strings of character entity references in the form &#nn or &#nnn, which display on a browser as the characters referred to. This should be more resistant to the screenscraper function of spambot address-harvesting tools because they lack the usual @ used to find e-mail addresses. It works in 9.x or later versions of the Windows operating system.
This tool appears to be unique in its capability to turn all mailto: address links found in any page in the directory the program starts in, or subdirectories if enabled into character entity reference strings in a single operation by the user.
Other possibilities for turning standard alphanumeric characters into character entity references include manual table lookup of individual characters or webforms on various site that allow manual entry of characters to be encoded into forms and generating individual hyperlinks via Submit.
Also mentioned briefly were a couple of other simple Windows web-authoring utilities that I recommend: the HTML Reference Library (a Windows help file with definitions of all current HTML tags) and the Color Wizard (which allows simple selection of background/link/text colors for a web page).