The pictures you are putting in the forum are attachments, which are limited to only 64 Kb so you have to may shrink them a lot, or compress them too much. If you put the pics on your own server (if you have one), and then use a reference to it in your post (use IMG button) it will show up, and you can use any size pic you like, and multiple pics per post.
Also, Microsoft Photo editor sounds quite crap, many people use Paint Shop Pro', a fairly professional but simple to use package for photo editing etc.
Can you change the compression level in Photo Editor? When you save, you may have an Options button, then you can reduce the compression.
Your pics seem to shrink rather poorly - this is definitely Photo Editor's problem. Get paint shop pro, you could even pay for it after 30 days or whenever, much simpler to obtain someone else's license code and use that instead
later!