yup all you got to do is compress it. you can use winzip or winrar.
youre folder shuold be maximum 8.5MB - then zip it, it might come to be about 8.2 MB
then attach it and send. the thing is that the attachment should not exceed 10MB, as yahoo does not permit it, and if your file is 8.2MB, after the virus scanning, the size will mysteriously increase to 9.5MB or so.
thus if your zipped file is 9.5MB to begin with you'll have a larger than 10MB file after scanning, and thus unable to send the attachment.
tip- what to do if the attachment is more that 10MB
simple - zip your folder. let is attain whatever size. then use a file splitter to split the files.use this link
http://www.filesplitter.org/
split your files to 8B size and attach them and send. the receiver should then splice up the files and unzip and view the attachment.
all the best. hope it helps you.