In Windows XP you find the unpXXXXXmdmp files in:
C:\Documents and Settings\All Users\Application Data\AVAST Software\Avast\log

You have to show hidden files and folder.
Start > Control panel > Folder options > View tab > Files and folders > Hidden Files and folders > Show files and folders. Apply and OK.

Compress the file with ZIP, RAR or 7Zip and give it an original name (lordFRZASCANunpmdmp). Add a text (use notepad) with your Forum e-mail and URL of this post.

Open Windows Explorer and copy/paste this address:

ftp://ftp.avast.com/incoming

Drag/drop compressed dump file into the right open window. Wait for transmission to conclude.