TIP:
To handle tar (zip lha 7z) archives, it is possible to use a program called file-roller...
http://maemo.org/packages/view/file-roller/

And then add some lines to mimehandling.conf like these for each extension you want.

.tar.gz=file-roller @ &
.tgz=file-roller @ &

However, if you prefer ease of fingeruse, and dont bother by files outside of /home/user/MyDocs/ then you can do the same with Xarchiver too.

.tar.gz=xarchiver @ &
.tgz=xarchiver @ &

Or, if you just want to unpack the archive without questions, then do.

.tar.gz=tar -xvzf @
.tgz=tar -xvzf @

The lack of a & at the end means that deskypplet will wait for the command to finish...