To post images for people on the forum to see, the best way is via a link to the image. Remember an image placed in the post will mean those on a slow connection will have problem just reading the forum because of the photo.
You'll need to upload your photos to a photo sharing place such as Photo Bucket, http://photobucket.com/ - it's free!
Here's what I did:
1. I Registered then straight away I was able to upload images.
2. I reduced size to 800x600 in drop down menu under where you upload, this gives a good size without someone waiting forever to see your photo.
3. To show a clickable thumb in the post only and on click it goes to photobucket to show the large size, select all the text in the box next to 'IMG thumb' then copy this address into your post. Or to show the full size image in the post click on 'IMG code' and copy and paste into the post.
I found this pretty painless and very easy.
There's other sites you can try: