I know but cant help if some people have failed to update.
That's a problem most of us have. But to save on sanity (and considering the fact that Microsoft is already previewing IE10), the majority of us have stopped supporting IE6 altogether. Microsoft encourages updates, and future versions of WordPress will stop testing for the old system pretty soon, too.
So while my first recommendation would be to advise these patients to update to IE8 (which works fine on Windows XP and is, in fact, the browser recommended by Microsoft, I recognize that might be impossible for some of your users.
But please also understand that the developers of TwentyTen aren't going to go back and build out support for IE6. Your safest bet would be to create a child theme for TwentyTen that uses conditional comments to load an additional stylesheet for IE6.
You can probably track down the lines of CSS causing problems for IE6, then just override/remove them in your conditional stylesheet to make things work in that browser. Just remember that you'll never get the IE6-compatible version to look/function exactly the same as the normal version.
There's a good tutorial on IE conditional stylesheets here.
And here is the "Universal Internet Explorer 6 Stylesheet" that might solve some problems, too.