Bitmaps (bmp files) don't show up in the preview, Andy. Jpegs (jpg files) are the best for loading here - they are the smallest.
To do all your image resizing in order to fit the file size limit, download the latest copy of Irfanview (
http://www.irfanview.com) from the website. It's the best file viewing software around, and it's completely free for private and educational use. You can crop your pictures in Irfanview, too.
You can't attach two picture on the same post at the moment. The only way to do this presently is to dump the pictures into a powerpoint or word file, and then do a screen grab from there of both together, save the screen grab as a jpg file, and then post that. It's a bit of a faff, but you can annotate the pictures as much as you like that way, and stop them spilling out of the frames.
For doing screen grabs, I use PaintShop Pro 7.
I'd better sign off before I appear to be more up on this stuff than I really am. It's all trial and error stuff by a complete amateur, but then that fits with my running ethos, too.