Making a web app for co-creator model unavailable to IE browsers

I'm making a web app to help buyers to design the texture of a co-creator model. The problem is that I'm using HTML5 and CSS3, but they are not fully supported by Internet Explorer, save the next IE9 that won't be available for Windows XP!?. I have tried to make something for IE8 with the help of Excanvas, but I would have to remove many of the options available to users with Firefox, Opera or Safari browsers (have to check Chrome).

So I'm thinking about taking into account both types of users in the future co-creator form using:
- A field to upload the image designed by the user with the web app using a browser capable of HTML5 & CSS3.
- Several fields to enter the elements required for the texture. I would make the final texture with the web app following the recommendations of the client, but this method doesn't ensure a result just as the client wants.

Checking recent browsers statistics, around 60% of users are using IE, but if you discount old versions (6, 7), the quota decreases to less than 50%. One solution for IE users would be to download a portable version of Firefox or Opera (I'm not sure about Safari) that could be removed without problems once the web app has been used. I have added a poll to this entry to know the opinion of the people, at least the people that participate in this forum.

I don't want to extend this post talking about why I haven't used other web technologies for the app such as Flash, Java, etc., but I'll answer any question about this topic for the interested ones.

I'm working on some apps using Processing, have you thought about that. You end up with a java applet but it's much easier than java.

Processing look very interesting and, as you say, it's easier than Java, but for this project the client have to enter text/image, select a font/color, sizes... I think that Processing doesn't have these things or at least in an easy way. For the interface I'm using Yahoo UI (YUI) and its color picker is perfect for selecting colors. But if processing is able to access the web elements and know when they change, I can use Processing for the graphical part and YUI for the interface.

Anyways, and this is other topic, it will be interesting to check if Processing can be used for the 3D preview of the models in Shapeways. There are contributed librarys to import STL and other 3D formats, and Processing can draw 3D using OpenGL, but I don't know if Processing can get parameters from GET/POST or <APPLET> once converted to an applet.