Hi Martin,
When loading photos as an attachment they are very limited in size (kb's) hence the small size, these restrictions are put in place by my forum host, not me, and I can't change them.
To post larger photos you will need to store yur photos in a photo storage site like Photobucket or Picasa for example, these sites are free to use and allow you to store an enormous amount of photos. Once stored it is a simple matter to tranbsfer your photos from your storage site to the forum by using the photo URL, the photo will be posted on the forum at 600 x 600 but a simple click will enlarge it to what ever size the original photo is. Naturally, if you store your photos smaller than 600 x 600 they will only be posted on the forum at the size you saved them as.
Most photo sharing sites are very easy to use and have the option to store your photos privately or you can share them with the rest of the world, your choice. I use Picasa, it is a really easy site to use, I have never had an issue with the site and photos transfer instantly, our members use a variety of photo sharing sites so it is up to you which one you would prefer.
Des.