nevica, open your windows explorer to the windows/minidump folder. Holding down the ctrl key, mouse select (left-click) each file you want to copy. Once you have them all selected, position the mouse over one of those selected and right-click. Choose COPY from the list.
Now go to the "my documents" folder and on the right hand side pane of windows explorer, right-click in an open part of the window and select PASTE. Now with the mouse still over these newly pasted files right-click again and select Send to > Compressed (zipped) folder
This should create a single zip file of all the dmp files. Then you go to the forum thread and hit the "Go Advanced" button. In the advanced window click on the paperclip and in the upload window browse for the my documents\minidump.zip file you created. Select OK and upload. close the upload window when it finishes and then write a little message to go with the attachment.