2) You can open MS Paint or sth. to paste or load the screenshot, and cut it's size by marqueeing the section you want. copy the section, => ctrl n => ctrl v => Resave as GIF.
3) Upload Image
when u reply to the thread, just click on "Attachments". Upload the file and afterwards choose it from "Attachments"
You can also attach older charts from the thread. You just need to know the attachment ID.
either get that from the old post using "quote", or, if u move your mouse over a shrinked image in a post and look for the ID in the URL.
If u click on the paperclip in the top right corner, u can see all attachments from the thread and can also get the attachmentIDs there by hovering over them
4) I suggest SnagIT, there are free versions (version7) floating through the web. It can capture everything you want.
Cheers