The limit for attachments on the forum is 2 MB
(according to WDZ's reply to Maximum Upload Size), when you try to attach a bigger file it won't get attached. (although there is no error message when the attachment file size is above the maximum limit, AFAIK)
And I don't believe you seeing attachments as big as 7mbs on here
Just upload it to a
file host and link to the file in your post, like Sunshine suggested.
And for the image, you have to use the direct link to the picture when you link it with [img][/img] tags, either like this:
code:
[url=http://img169.imageshack.us/img169/8011/att00001yd2.png][img=202x110]http://img169.imageshack.us/img169/8011/att00001yd2.png[/img][/url]
or like this, using the imageshack preview:
code:
[URL=http://img169.imageshack.us/my.php?image=att00001yd2.png][IMG]http://img169.imageshack.us/img169/8011/att00001yd2.th.png[/IMG][/URL]