You won't be able to. The software that the forum is running is a bit older, and file upload from the iPad actually has to be built into a website/application by the developer. I'm not sure whether the newer version of this software has this feature, but I doubt it. What you can do, however, is download some app that does allow you to upload images to some place. The CloudApp service allows you to do this, and then you can post the link in a post here. You can even have the image display in a post by clicking the little mountain icon and then pasting the image URL in there.
You should be able to do it the same way you do on a computer, assuming you're running iOS 6. I'm able to do it from my iPad
U click show all albums then upload picure and then the gray button thingy and then choose which picure and then dicripition I only go on here on my iPod and I have the max amount of pics so ...
Cheers folks. Sorry I didn't respond sooner, I forgot about this question. I was specifically talking about posting images in forum posts, which I don't seem to be able to do. I'll have a look at the apps. Thanks again.
I pretty much only use my iPad when on this forum, (its replaced my laptop) I just post it on an "imaging hosting" site and paste the link in my reply