Google is your friend! I searched for "create your own windows font" and I got
http://www.high-logic.com/fcp.html, it has a free trial version (doesn't mention whether the "save" feature is disabled in the trial version) and $50 to buy, I didn't download it but just from the screenshots they have it looks pretty nice. I also found
http://www.fontsnthings.com/tools/creation.html which lists several software packages, they might have some free ones but I didn't check them all out. Also it seems most of them allow you to load a .bmp for the particular character (probably would make it easier since you want to use smileys), so what might be the easiest is to create the smiley in an image editor (I'd recommend GIMP
www.gimp.org/win32, which has 90% of the power of Photoshop, but 0% of the cost,ideal for someone who doesn't like to use warez but also realizes he can't afford everything
) Then import that .bmp into the font editor.
Hope that helps.