Not a problem
The text box that I get is the same type of box that I get on this screen when I move my cursor to "Post Reply". The cursor changes and a small text box appears that reads "Reply".
What you are seeing is perfectly normal - I see the same in IE8 on Win 7 Pro x64 - they are effectively Tooltips' and are coded into the page. The cursor changes to a hand icon when over the Post Reply button (and others), but the tooltip - Reply' is below the cursor - see screenshot.
If you are seeing some displacement of the cursor and tooltip I would try ....
Set IE 8 to run in Compatability Mode - Page > Compatability Mode Settings
Check that you have the latest software for your mouse
And if the problem remains update your graphics drivers, although I don't think that is the issue.