Pretty sure you can. The is vBulletin software, and if you go to Post Reply or Go Advanced you'll see the Manage Attachments button. You can see I've uploaded a text file attachment here. Just ensure you zip your file. If you are using Windows XP, just right click the file and select Send To, then choose Compressed Folder, then just attach that folder to your reply. Make sure the file is slimmed down so when it zips it will be under the size restriction (2.86 MB).