Here is a quote from the Lawnsite F.A.Q. maybe it will help you.
"The administrator may allow you to use the attachment feature of this board, which gives you the ability to attach files of certain types to your posts. This could be an image, a text document, a zip file etc. There will be a limit to the file size of any attachments you make, as the board should not be used as an extension of your hard disk!
To attach a file to a new post, simply click the [Browse] button at the bottom of the post composition page, and locate the file that you want to attach from your local hard drive.
Only certain types of files may be attached: these are the valid file extensions for files to be attached to this board: htm html gif jpg jpeg png txt zip bmp jpeg doc xls pdf.
After posting, the attachment will show up in the body of your message. To view the contents of the attachment (if it is not already displayed) simply click the filename link that appears next to the attachment icon ."