[Suicide Junkie]

When you're typing a post, right below your password box is an attachment box.
Don't fill in anything there, but click the link right beside it "Upload your files"

Enter your Login/Password if required, and browse to your files.
Click "upload", and wait
The "file upload manager" window will eventually go to a blank white box, or say "upload successful" once that happens, your upload is successful, and you can close the manager.

The attachment field will read something like "437214.txt". This is GOOD, don't change it. That text file lists all of the various files to include in your post.

When you post, there'll be file icons down the right side of your text.