I noticed the same problem when I had a small photo of me next to the descriptive in my signature, and it caused EVERY page to need left/right scrolling.
There are a few Avatars too which cause this problem - I may need to shorten the width a little to make the scrolling issue resolve. But this is a quirk in Explorer, since Netscape, Fire Fox and Mozilla wrap properly. I even tried different TEXT sizes and none eliminated the Explorer problem here.
So I took my photo off (it wasn't a great one anyways - lol) but I'll redo my signature image to be smaller, have a photo and a bio - something that isn't as big, I'd hate to start a trend WHICH I see in many forums. Some have unimaginable huge signature images which cause you to scroll endlessly to get through a handful of posts. I just can't tolerate that here, it is just inconvenient to readers and cause long download times for dial-uppers.